MR Glossary
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Acquisition
MR measurement technique. Data acquisition
during MR imaging. To improve the signal-tonoise ratio in the image, several acquisitions can
be performed to image a slice. At the same time,
they are averaged during image reconstruction
(averages).
Acquisition matrix
–> Raw data matrix
Acquisition time (TA)
MR measurement technique. Measurement
time for an entire data set.
Acquisition window
MR measurement technique. The time frame
in a pulse sequence during which the MR signal
was acquired.
Active shielding
Magnetic field: For strong magnets, the stray
field has to be actively shielded to increase the
safety zone. For this purpose, secondary compensating coils are attached around the magnet
opposite the primary field-generating coils.
Gradients: Gradient systems with opposed coils
to reduce eddy currents.
TA:
Time to Acquisition
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Active shim
Quality assurance. Shim by adjusting the currents in the shim coils.
Adaptive Combine
Measurement parameters. Algorithm for combining the channels of MR signals from several
receiver coils. Adaptive Combine improves the
measurement results for most measurement
protocols.
ADC image
Diffusion-weighted imaging. ADC images
can be reconstructed from diffusion-weighted
images with at least 2 b-values. The contrast
corresponds to the spatially distributed diffusion
coefficients of the acquired tissue and does not
contain T1 or T2* portions.
Aliasing artifact
Image quality. Aliasing artifacts are generated
when the measurement object is outside the FoV
but still within the sensitive volume of the coil.
Signals from outside the FoV overlap the image,
but on the opposite side. Caused by the sampling
and subsequent Fourier transformation of signal
components above the Nyquist frequency. Reme-
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died primarily through oversampling, but
regional presaturation may be used as well.
Analog-to-digital
converter (ADC)
MR components. Part of the computer system
which converts the analog MR signal into a digital signal.
Array coil
MR components. An array coil combines the
advantages of smaller coils (high signal-to-noise
ratio) with those of larger coils (large field of
view). It consists of multiple independent coil
elements that can be combined depending on
the requirements of the examination.
–> Integrated Panorama Array (IPA)
Array processor
MR components. An array processor comprises
multiple computer and storage units that are
switched in sequence and in parallel while simultaneously performing a computing task. Core of
the image reconstruction system.
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ART
Image reconstruction. Three-dimensional technique for fully automatic motion correction. To
minimize motion errors, the 3D data sets are
shifted, rotated, and interpolated to correspond
closely to a reference data set.
ART:
Advanced Retrospective
Technique
Arterial Spin Labeling
(ASL)
Perfusion imaging. Arterial Spin Labeling uses
the water in arterial blood as an endogenous
contrast agent by marking a specific vessel with
an RF pulse. By subtracting images with/without
markings, statements about the relative blood
flow can be made. This technique allows insight
into perfusion and the functional physiology of
the brain. ASL is suitable for evaluating tumors,
degenerative diseases and seizure disorders, as
well as neuro-scientific research, e.g., for examining functional changes in the blood flow of the
brain.
ASL:
Arterial Spin Labeling
Artifact
Image quality. Signal intensities in the
MR image that do not correspond to the spatial
distribution of tissue in the image plane. They
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result mainly from physiological as well as
system-related influences.
–> Aliasing artifact
–> Distortion artifact
–> Flow artifact
–> Motion artifact
AutoAlign Head LS
Slice positioning. Automatic orientation of the
slice position, applicable for head examinations.
Independent of patient positioning, the MR system automatically performs reproducible slice
positioning and simplifies as well as accelerates
examination planning. Uses bony structures as
anatomical orientation points.
AutoAlign Spine
Slice positioning. Automatic positioning and
double-orthogonal orientation of transverse slice
groups during examination of the spine based on
the anatomical conditions of the intervertebral
disk. Allows for easier and faster examinations
with a better and standardized image quality.
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Auto-calibration
MR measurement technique . When using
Parallel Acquisition Techniques (PAT), coil profile
information required for reconstruction is
obtained via a calibration measurement.
Auto-calibration is integrated into the measurement and is both faster (approx. 1 second) and
more exact than a separate calibration. It is performed with sequence characteristics that are
identical to the acquisition and for the current
patient position (including possible motions).
Averages
Measurement parameters. Mean value of measured signals in a slice to improve the signal-tonoise ratio. Averaging is performed, for example,
on a measurement with 2 acquisitions.
Axial
–> Orthogonal slices
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Bandwidth
Measurement parameters. Frequency spectrum
(minimum to maximum processed frequency) of
a pulse sequence acquired by an RF system.
–> Readout bandwidth
–> Transmission bandwidth
Baseline
BOLD imaging: Non-activated image, in contrast
to activated image, refer also to paradigm.
MR spectroscopy: Background signal from
which the peaks rise.
Baseline correction
MR spectroscopy. Post-processing of the spectrum to suppress baseline deviations from the
zero line.
Basic image
Measurement. Image selected as the default
for slice positioning; localizer, scout.
Post-processing. Image measured for postprocessing; for example, MIP or MPR.
BEAT
Cardiac imaging. syngo tools to optimize
cardiac examinations with a few mouse clicks.
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BLADE
MR measurement technique. The BLADE technique helps reduce the motion sensitivity of MR
examinations: BLADE is available for the TurboSE
sequence. Each echo train of the sequence
generates a low resolution image with a phaseencoding direction rotated from one excitation to
the next. Subsequently, the individual, low-resolution images are combined into a high-resolution image.
Body coil
MR components. The body coil is an integral
part of the magnet. It functions as a transceiver
coil. It has a large measurement field, but does
not have the high signal-to-noise ratio of special
coils.
BOLD effect
BOLD imaging. During increased neural activity,
oxygen concentration increases in the venous
blood volume. Local blood flow increases as well.
As oxygen increases, the magnetic characteristics of erythrocytes approximate that of the surrounding blood plasma. Transverse magnetization in blood vessels decays more slowly. This
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BOLD effect extends T2 and T2*, measurable as
an increase in signal in the blood volume under
examination.
BOLD imaging
MR application. BOLD imaging uses local
changes in blood flow to indicate the current
level of activity in a region of the brain. Hydrogen
protons in human blood are the signal carriers.
Blood works as an intrinsic contrast agent:
local concentrations of oxygen associated with
changes in blood flow are measured (BOLD
effect).
Bolus
Examination with contrast agent. Partial volumes in a vascular section. A small amount of
contrast agent transported by blood flow whose
spread is tracked (Bolus Tracking).
BRACE
MR mammography. Methods for soft-tissue
corrections with MR mammography. Eliminates
motion artifacts during dynamic imaging.
BOLD:
Blood Oxygenation Level
Dependent Imaging
BRACE:
Breast Acquisition Correction
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Breathhold technique
MR measurement technique. To avoid respiratory artifacts, the patient holds his breath during
the entire measurement. Suitable for use in
abdominal and cardiac examinations. Not suitable for use with uncooperative patients, small
children, or anesthetized patients.
Bright-blood effect
Image quality. Brightly-displayed blood, as an
effect of slow flow. Vascular spins are completely
replaced by unsaturated spins during repetition
time TR. In gradient echo sequences, the signal
is maximum, and blood is displayed bright in the
MR image.
The effect is used in bright-blood imaging of
the heart for dynamic display of blood flow, an
effect that is similar for ToF angiography.
b-value
Diffusion imaging. Diffusion weighting factor.
The higher the b-value, the stronger the diffusion weighting.
B0 field
MR physics. The static main magnetic field of a
magnetic resonance system.
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B1 field
MR physics. The alternating magnetic field of
RF radiation generated by a transmitter coil.
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Cardiac imaging
–> MR cardiology
Cardiac triggering
Physiological imaging. Cardiac triggering
prevents or reduces motion artifacts in the
MR image caused by the heartbeat or pulsating
blood flow. Triggering enables MR images to be
acquired synchronized to cardiac movement.
ECG and pulse triggering enable precise functional examinations of the cardiovascular system
and the CSF in the head and spine. Major vessels,
the myocardium, and blood flow can be displayed.
Cardio
–> MR cardiology
Care Bolus
Contrast-enhanced MRA. Using Care Bolus,
the center of the Fourier space is measured as
quickly as possible once the contrast agent
reaches the region to be examined. This ensures
optimal contrast of arterial vessels.
Center
–> Windowing
CARE:
Combined Applications to
Reduce Exposure
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Chemical shift
MR physics. Shift in the resonance frequency of
an atomic nucleus depending on the chemical
bonds of the atom or structure of the molecule.
Caused primarily by a weakening of the applied
magnetic field by the electron shell, and is proportional to the magnetic field strength. Units:
1 ppm of the resonance frequency.
Chemical shift
artifact
Image quality. With gradient echo sequences,
the chemical shift may lead to “phase cancellation” in the image. The cause are the slightly
different resonance frequencies of fat and water
(approx. 3.5 ppm), which lead to a phase shift
in a voxel containing fat/water. In an opposedphase image, contour artifacts may appear at the
interface of fat and water-containing tissue.
Chemical shift
imaging (CSI)
MR spectroscopy. In contrast to single volume
spectroscopy, the two CSI methods map the
metabolic information from a Volume of Interest
(VoI) in a spectral matrix. The spatial encoding
requires a minimum measurement time of several minutes.
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Cine
Image display. To display dynamic processes,
such as cardiac movement. The MR images run
automatically through the active screen segment, either in a cycle or forward and backward
(yoyo).
CISS sequence
MR measurement technique. Strong
T2-weighted 3D gradient echo technique with
high resolution, where two acquisitions with different excitation levels are performed internally
and subsequently combined. Prevents streaks,
for example in the inner ear. Post-processing
with MPR or MIP.
Coil profile
Physics. Receiver signal homogeneity of an
RF coil, also known as coil sensitivity profile. The
strength of the MR signal received from a voxel
depends on the voxel location relative to the coil.
In general, the signal is greatest in the vicinity of
the coil. The farther away the voxel is from the
coil, the weaker the signal.
CISS:
Constructive Interference in
Steady State
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The coil profiles can be obtained either from a
separate calibration measurement or via an autocalibration integrated into the measurement.
Coils
–> RF coils
Columns
MR measurement technique. The frequencyencoded portion of the measurement matrix.
–> Rows
Concatenation
Measurement parameters. Distributing the
slices to be measured over multiple measurements. Possible applications:
• For a short TR, increase the number of concatenations to be able to measure more slices.
• To prevent cross talk when the slice distance is
short, set concatenations to 2 and use an interleaved slice sequence.
Contour artifact
–> Chemical shift artifact
Contrast
Image quality. Relative difference in signal
strength between two adjacent tissue types.
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Contrast agent
Image quality. Chemical compounds to improve
contrast. For MR, normally paramagnetic contrast agents, such as Gadolinium DTPA or other
Gadolinium compounds are used.
In contrast to X-ray techniques, where contrast
agent is directly visible, in MR, contrast agents
have an indirect effect only; they reduce the
relaxation times for water in tissue.
Contrast-enhanced
MR angiography
(CE MRA)
MR application. Contrast-enhanced MR angiography utilizes the T1 reduction of blood through
Gadolinium-based contrast agent. Since CE MRA
is not limited by saturation effects, it allows for
large measurement fields and any orientation.
Contrast-to-noise ratio
(CNR)
Image quality. The contrast-to-noise ratio in the
MR image is the difference of the signal-to-noise
ratios between two relevant tissue types, A and
B.
CNR = SNRA – SNRB
Coronal
–> Orthogonal slices
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CP coil
MR components. Circularly polarized transmission or receiver coil with two orthogonal transmission and/or receiver channels, also known as
quadrature coil. A receiver coil has a better signal-to-noise ratio than a linearly polarized coil.
Cross-talk
Image quality. If slices are too close, the signals
from adjacent slices affect one another, especially when the slice distance equals 0. Caused by
a slice profile that is not ideal due to the constraints of the measurement technology. Cross
talk effects T1 contrast.
Remedied primarily using an interleaved slice
sequence.
Cryogens
Magnet technology. Cooling agent to maintain
the superconductivity of the magnet (liquid
helium or nitrogen).
CP:
Circularly Polarized
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Dark Blood
Cardiac imaging. Special preparation pulse that
saturates the blood; for displaying cardiovascular
anatomy.
Dark-fluid imaging
(FLAIR)
MR measurement technique. Turbo inversion
recovery technique with a long effective echo
time and long inversion time to suppress fluids.
Lesions that are normally covered by bright fluid
signals using conventional T2 contrastare made
visible by the dark-fluid technique. The inversion
pulse is applied such that the T1 relaxation of the
fluid reaches zero crossing at time point TI,
resulting in the signal being “erased”.
dB/dt
MR physics. Formula for the temporal change
of the magnetic field, read “dB over dt”. Using
alternating magnetic fields, electrical fields are
generated in conductive material, such as human
tissue. These fields may induce electrical current
in the patient's body.
dB/dt is an important value for safety
thresholds.
–> Stimulation
FLAIR:
Fluid Attenuated Inversion
Recovery
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Defocussing
–> Dephasing
Delay time
–> Trigger delay time (TD)
Dephasing
MR physics. After RF is applied, phase differences appear between precessing spins, resulting in a decay in transverse magnetization.
Caused primarily by spin-spin interaction and
inhomogeneity in the magnetic field, can also
be caused by switching specific gradient fields
(flow dephasing).
–> Rephasing
DESS sequence
MR measurement technique. DESS is a 3D
gradient echo technique where two different
gradient echoes (FISP sequence and PSIF
sequence) are acquired during repetition time
TR. During image reconstruction, the strongly
T2-weighted PSIF image is added to the FISP
image. Use: Joints, good contrast for cartilage.
Post-processing with MPR.
DESS:
Dual Echo Steady State
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Diamagnetism
MR physics. Effect resulting in a slightly weakened magnetic field when a substance is introduced into it. Magnetization of a diamagnetic
material is opposite the main magnetic field. The
material is considered to have a negative magnetic susceptibility (magnetizability).
DICOM
Standard for electronic data exchange of medical
images.
The DICOM standard enables the transfer of
digital medical images and corresponding information, independent of device and manufacturer. In addition, DICOM provides an interface
to hospital systems based on other standards.
Diffusion
Physics. Process by which molecules or other
particles move from areas of higher concentration to areas of lower concentration. When concentrations are equal, there is a statistical balance, even though the molecules are constantly
under thermal movement (Brownian molecular
movement).
DICOM:
Digital Imaging and
Communication in Medicine
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Diffusion contrast
Diffusion imaging. The diffusion of water
molecules along a field gradient reduces the
MR signal. The behavior is exponential:
Signal = S0 exp(−b D)
In areas of low diffusion (pathological tissue),
signal loss is less intense. These areas are shown
brighter.
Diffusion tensor
Diffusion imaging. Physical magnitude which
takes into account the directional dependency
of diffusion. The diffusion tensor displays the
mobility of water molecules in all three coordinates. The tensor data are used as the basis for
computing additional maps (e.g., FA map) or
diffusion tractography.
Diffusion tensor
imaging (DTI)
MR application. Method for displaying the directional dependency of diffusion. Application:
examinations involving the architecture, configuration and integrity of nerve fiber bundles (neurological research).
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Diffusion tractography
Diffusion tensor imaging. Method for displaying diffusion tracts using diffusion tensor measurements.
Tractography supports the planning of operations and supports neurophysiological research
regarding the connectivity and pathology of the
white matter.
Diffusion-weighted
imaging
MR application. MR imaging is sensitive to
motion and flow and to the relatively low diffusion effect, when the gradients are strong
enough. Diffusive movements in tissue (e.g., natural diffusion of water) reduce the signal.
Of interest are regions where diffusion is
reduced compared to its surroundings (such as
cell membranes, along white matter tracts, or in
areas of the brain affected by stroke). Reduced
diffusion means the reduction in signal is less
intense: the affected regions are displayed
brighter in the image.
Diffusion weighting
factor
–> b-value
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Distortion artifact
Image quality. Image distortions are caused by
inhomogeneity in the magnetic field, gradient
non-linearity, or ferromagnetic materials in proximity to the examination.
Dixon technique
MR measurement technique. Dixon is a technique for separating fat and water. For this purpose, the technique uses the different resonance
frequencies of fat and water protons (chemical
shift). Essentially an in-phase and an opposedphase image are measured. By adding the inphase and opposed-phase, pure water images
are generated while pure fat images are generated through subtraction.
Double-contrast
sequences
MR measurement technique. TurboSE counterpart to double-echo sequences, generally 5 times
as fast.
To keep the pulse train as short as possible,
only echoes for PD- and T2-weighted images
where the phase-encoding gradient has a small
amplitude are measured separately. The echoes
that determine resolution are used in both raw
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data matrices (echo sharing). This reduces the
number of echoes required. More slices can be
acquired for the TR specified, and the RF stress
(SAR) drops.
Double-echo sequence
MR measurement technique. Spin-echo
sequence with two echoes. In addition, proton
density weighted images are generated without
increasing the measurement time. They are produced from the first echo of a T2-weighted double-echo sequence.
Double-oblique slice
Slice positioning. Obtained by rotating an
oblique slice about one axis in the image plane.
Duty cycle
Gradient technology. Time permitted during
which the gradient system can be run at maximum power. Based on the total time (in %),
including the cool-down phase.
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Eccentricity
–> Off-center
ECG triggering
Physiological imaging. ECG triggering synchronizes the measurement with the cardiac signal
of the patient. The R wave is used as the trigger.
This method is particularly useful for measurements of the heart or thorax, because images
can be blurred due to cardiac contractions.
Echo
MR physics. The MR signal generated by an RF
or gradient pulse.
–> Gradient echo
–> Spin-echo (SE)
Echo-planar imaging
(EPI)
MR measurement technique. Extremely fast
MR technique where the complete image is
obtained using a single selective excitation pulse.
Field gradients are switched periodically
to generate a series of gradient echoes. An
image of the excited plane is obtained by using
a Fourier transformation on the resulting echo
train.
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Echo sharing
MR measurement technique. For double-contrast sequences. Echoes that determine image
resolution are used in both raw data matrices.
Echo spacing
MR measurement technique. Distance
between two echoes; e.g., TurboSE or EPI
sequences. A short echo space produces compact sequence timing and fewer image artifacts.
Echo time (TE)
Measurement parameters. The time between
the excitation pulse of a sequence and the resulting echo used as the MR signal. Determines
image contrast.
Echo train
Multi-echo sequences. Two or more echoes in
sequence; each of them obtains a different
phase-encoding direction.
Eddy currents
MR measurement technique. Electrical currents
generated in a conductor by changing magnetic
fields or movement of the conductor within the
magnetic field. Can be reduced using shielded
TE:
Time to Echo
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gradients. Eddy currents are a source for artifacts.
Edge oscillation
–> Truncation artifact
Effective echo time
(TEeff)
MR measurement technique. The contrast and
signal-to-noise ratio of an MR image are determined primarily by the temporal position of the
echo where the phase-encoding gradient has the
smallest amplitude. In this case, the echo signal
undergoes minimal dephasing and has the strongest signal. The time period between the excitation pulse and this echo is the effective echo
time.
Effective repetition
time (TReff)
Physiological imaging. For prospective cardiac
triggering, repetition time TR cannot be set as
desired; rather, it is determined by the time interval for the trigger. The effective repetition time
TReff established by the trigger interval fluctuates
with the physiological rhythm.
TR:
Time to Repetition
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EPI factor
Echo-planar imaging. Number of gradient echoes of an EPI sequence acquired after a single
excitation pulse (typically 64 to 128). EPI factor
128 means a measurement time 128 times faster
than a normal gradient echo sequence.
EPI technique
–> Echo-planar imaging (EPI)
Ernst angle
MR measurement technique. The flip angle
(< 90°) of a gradient echo sequence where a tissue with a specific T1 generates its maximum
signal. Depending on the repetition time TR.
αErnst = arccos (e–TR/T1)
Excitation pulse
MR measurement technique. The equilibrium
of the spins in the magnetic field is distorted by a
brief RF pulse. The higher the energy of an excitating RF pulse, the greater is the tip angle of the
net magnetization. The tip angle of the magnetization at the end of the RF pulse is known as the
flip angle.
EPI:
Echo-Planar Imaging
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FA map
Diffusion imaging. An FA map displays the
anisotropic character of the diffusion in relationship to the average overall diffusion.
Isotropic diffusion: Water molecules move the
same way in every direction.
Anisotropic diffusion: The water molecules
clearly move in a preferred direction.
Isotropic diffusion is displayed dark, anisotropic
diffusion is displayed bright. The color encodes
the orientation of diffusion. The FA map is one of
the parametric maps for diffusion tensor imaging.
Fast Fourier
Transformation (FFT)
Image reconstruction. Algorithm for fast
MR image reconstruction from raw data.
Fat image
A pure fat image only displays the signal from fat
protons in the image and suppresses the signal
from water protons. Is generated with the Dixon
technique, for example.
FA:
Fractional Anisotropy
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FatSat
–> Fat saturation
Fat saturation (FatSat)
Image quality. To suppress the fat portion in the
MR signal, the fat protons are saturated by frequency-selective RF pulses. The fat saturation
depends on the homogeneity, the chemical shift
is 3.5 ‚ppm.
–> Presaturation
Fat suppression
Image quality. The MR signal comprises the sum
of signals from water and fat protons. Different
techniques are used to suppress the fat signal.
–> Fat saturation
Feet First
Positioning. The patient is positioned feet first in
the magnet bore.
Ferromagnetism
Physics. Effect where a material, e.g., iron is
drawn toward a magnetic field. Relevant to
safety for MR imaging.
FID signal
MR physics. Signal induced by the RF excitation
of the nuclear spins, and that decreases expo-
FatSat:
Fat Saturation
FID:
Free Induction Decay
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nentially without external influence at a characteristic time constant T2*.
Field of View (FoV)
Measurement parameters. Base (square) size of
the slice to be measured (in mm). The smaller
the field of view, the higher the resolution, since
the voxels are smaller for the same matrix size.
Field strength
–> Magnetic field strength
Filter
–> Image data filter
–> Normalization filter
–> Raw data filter
FISP sequence
MR measurement technique. With the FISP gradient echo sequence, the remaining transverse
magnetization is not eliminated before the next
RF pulse. Instead, it contributes to the signal
along with the longitudinal magnetization. The
strength of longitudinal magnetization depends
on T1; the amplitude of transverse magnetization depends on T2*. Contrast is a function of T1/
T2* and is generally not dependent on TR.
FISP:
Fast Imaging with Steady State
Precession
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FLAIR technique
–> Dark-fluid imaging (FLAIR)
FLASH sequence
MR measurement technique. The FLASH gradient echo sequence uses the equilibrium of longitudinal magnetization. The remaining transverse
magnetization is eliminated by a strong gradient
(spoiler gradient). T1-weighted and T2*weighted contrast can be set with the FLASH
sequence.
Flip angle
Measurement parameters. The tip angle of
magnetization from the longitudinal direction at
the end of an RF pulse. Frequently used flip
angles are 90° and 180° flip angles.
Flow artifact
Image quality. Motion artifacts caused by local
signal changes during a measurement. For example, the inflow intensity of a vessel perpendicular
to the image plane changes periodically due to
pulsatile blood flow. In transverse body imaging,
ghosting appears in the aorta. Due to turbulent
blood flow in the heart, non-periodic inflow
enhancement results in smearing of the image.
FLASH:
Fast Low Angle Shot
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Flow compensation
(GMR)
MR measurement technique. To override the
signal loss caused by spin movement, both
moved and unmoved spins can be rephased.
Additional gradient pulses are switched in suitable size and time duration.
Flow dephasing
MR measurement technique. Exclusion of the
signal from flowing substances such as blood,
through the application of specifically applied
gradient fields.
–> Dephasing
Flow effect
Image quality. Flow effects play two conflicting
roles in MR imaging:
• Source of unwanted image artifacts
–> Flow artifact
• In MR angiography, displays blood vessels and
provides quantitative information on the velocity of blood flow.
–> Bright-blood effect
–> Inflow amplification
–> Jet effect
–> Signal elimination
GMR:
Gradient Motion Rephasing
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–> Washout effect
Flow encoding
MR measurement technique. Use of phaseencoding or other techniques to obtain information regarding the direction and velocity of moving material.
Flow quantification
MR application. Quantitative flow measurements using phase contrast to examine pathologies in large vessels or as part of an extensive cardiovascular MR examination. Flow
measurements enable the non-invasive evaluation of blood flow.
Flow rephasing
–> Rephasing
Flow sensitivity
(venc)
Phase-contrast angiography. The flow sensitivity of a phase-contrast sequence refers to the
flow velocity where the phase difference
between flow-compensating and flow-encoding
scans is 180 degrees.
fMRI
–> Functional imaging
venc:
velocity encoding
fMRI:
functional Magnetic Resonance
Imaging
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Fourier space
MR measurement technique. The axes of the
raw data matrix axes are known as kx and ky.
They divide the matrix into four squares. The
plane spanned by the two axes is called Fourier
space or k-space.
Fourier
Transformation
Imaging: Mathematical procedure for reconstructing images from raw data.
MR spectroscopy: Method for calculating
MR spectra from MR time data.
FoV
–> Field of View (FoV)
Fractional anisotropy
–> FA map
Free induction decay
–> FID signal
Frequency
Physics. The number of repetitions of a periodic
process in a unit of time (unit: Hertz).
Frequency encoding
MR measurement technique. During data
acquisition, a magnetic field gradient is applied
in one spatial direction, providing nuclear spins
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with linearly increasing precessional frequencies.
The readout MR signal is a mix of all these frequencies. These various frequencies must be filtered individually. In the row direction, the location of the nuclear spin can be reconstructed
from the frequency. This axis is called the frequency-encoding axis.
The perpendicular axis to it is the direction of
the phase encoding.
Frequency tuning
MR measurement technique. Setting the
RF system frequency to the resonance frequency
of the main magnetic field (Larmor frequency).
Functional imaging
–> BOLD imaging
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Gadolinium DTPA
Contrast agent. The uptake of gadolinium-containing contrast medium reduces the T1 and T2
values of tissues, depending on the concentration. The effect: T1 weighting increases, while
T2 weighting is suppressed. The T1 effect is the
more relevant in clinical routines.
Gauss
MR physics. Old unit for magnetic field strength.
Today, the unit Tesla (T) is used
(1 Tesla = 10000 Gauss).
Ghost images
Image quality. During periodic movement such
as breathing, some phase-encoding steps are
acquired during inspiration (e.g., inspiration
phase), and others during expiration (e.g., expiration phase). This quasi-periodic misencoding
results in a displaced false image of the body
region. Signal-rich structures like subcutaneous
fat are particularly susceptible to ghosting due to
movement. The distance between the ghost
images depends on the movement period and
relaxation time TR.
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During echo-planar imaging, ghosting may
occur at a distance of half the FoV.
Gibbs artifact
–> Truncation artifact
GLM
BOLD imaging. GLM calculates BOLD images by
adjusting a linear combination of different signal
portions. In addition, interferences such as slow
signal fluctuation are successfully suppressed
and reliable activation maps are obtained. GLM
also allows a detailed evaluation of the measurement data.
Global Bolus Plot
(GBP)
–> Global time-density curve
Global Shim
Quality assurance. For several techniques, such
as fat saturation, EPI or spectroscopy, especially
high magnetic field homogeneity is required. In
this case, shim coils can be used to optimize
homogeneity.
GLM:
General Linear Model
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Global time-density
curve
Perfusion imaging. Diagram for evaluating
successful bolus transport.
GRACE
MR spectroscopy. GRACE is a SVS procedure in
breast spectroscopy, used to quantify the cholin
signal.
Gradients
MR physics. A gradient defines the strength and
orientation of change of a magnitude in space.
A magnetic field gradient is a change in the
magnetic field of a certain orientation, a linear
increase or decrease. The magnetic gradient
fields are generated with gradient coils. They
determine, for example, the spatial resolution in
an image.
Parameters: rise time, duty cycle, gradient linearity, gradient strength, slew rate.
Gradient coils
MR components. Coils to generate magnetic
gradient fields. Gradient coils are operated in
pairs in the magnet, at the same current, however, of opposite polarities.
GRACE:
Generalized Breast
Spectroscopy Exam
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One of the coils increases the static magnetic
field by a certain amount, the opposite coil
reduces it by the same amount. This changes the
magnetic field overall. The change is the linear
gradient. According to the coordinate axes, there
are x, y, and z gradient coils. In connection with
the gradient amplifier, they form the gradient
system, used to precisely localize the requested
slice position.
Gradient echo
MR physics. Echo created by switching a pair of
dephasing and rephasing gradients, without a
rephasing 180° pulse as with the spin-echo technique.
Gradient Motion
Rephasing (GMR)
–> Flow compensation
Gradient strength
Gradient technology. Amplitude of the gradient field, measurement unit mT/m (millitesla per
meter).
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Gradient swap
Measurement parameters. Exchange of phaseencoding and readout directions in the image. As
a result, interfering flow and motion artifacts are
rotated by 90°. Prevents artifacts from covering
structures of interest.
GRAPPA
MR measurement technique. Further development of SMASH with auto-calibration and a
modified algorithm for image reconstruction.
Grid tagging
–> Tagging
GSP
Graphical positioning of the slices/saturation
regions to be acquired on base images (localizer
images). Relevant measurement parameters may
be conveniently adjusted on-screen via the
mouse.
GRAPPA:
Generalized Autocalibrating
Partially Parallel Acquisition
GSP:
Graphical Slice Positioning
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Half-Fourier matrix
MR measurement technique. The raw data
matrix has a specific symmetry which theoretically makes sampling of only half the matrix
sufficient. The other half can be symmetrically
reconstructed; mathematically, the matrices are
conjugated complexes.
However, unavoidable phase errors due to
minor magnetic field inhomogeneity require a
phase correction. For this reason, only slightly
more than half of the raw data are acquired.
Measurement time is reduced by just under
50 %.
Hanning filter
Type of raw data filter
HASTE technique
MR measurement technique. HASTE is a Turbo
spin-echo technique and is used for sequential
acquisition of high-resolution T2-weighted
images.
All image information is obtained after a single
excitation pulse. Echoes are generated by a subsequent 180° pulse The image is obtained after a
half-Fourier reconstruction.
HASTE:
Half-Fourier Acquisition
Single-Shot TurboSE
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Head First
Positioning. The patient is positioned head first
in the magnet bore.
Hertz
MR physics. SI unit of frequency
(1 Hz = 1 s−1).
Homogeneity
Image quality. A magnetic field is considered
homogeneous when it has the same field
strength across the entire field. With MR, the
homogeneity of the static magnetic field is an
important criterion for magnet quality. High
homogeneity is important for spectral fat saturation, a large field of view (FoV), off-center imaging, echo-planar imaging, and MR spectroscopy.
Hybrid spectroscopy
MR application. Combination of single volume
spectroscopy and chemical shift imaging. The
CSI measurement is performed across a selectively-excited volume of interest. Via volume
selection, areas with strong distorting signals
(e.g., fat) are not stimulated. For this reason,
they do not contribute signal to the spectra.
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Image contrast
Image quality. The contrast in the image is the
relative difference in the signal strength between
two adjacent tissue types. It depends primarily
on the existing tissue parameters T1, T2, proton
density) and, in the case of MRA, on the flow as
well.
Contrast can be affected by the sequence used
(spin echo, inversion recovery, gradient echo,
TurboSE etc.), the measurement parameters (TR,
TE, TI, flip angle) and the use of contrast agent.
Image data filter
Reconstruction parameter. Filters of various
strengths (strong, medium, soft) can subsequently be applied to MR images to reduce noise.
High pass and low pass filters are used with different shapes to the characteristic curves. Other
filter types include, for example, smoothing
filters.
Image manipulation
Post-processing. MR images can be manipulated
in various ways for manipulation. The gray scale
of the images—either in its entirety or in
sections—can be modified as desired (e.g., addi-
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tion, subtraction, averaging, rotation, flip, offset,
inversion).
Image matrix
Image display. The MR image consists of a multitude of picture elements (pixel). Pixels are allocated to a matrix in a checkered pattern. Every
pixel in the image matrix displays a specific gray
scale level. Viewed as a whole, the matrix of gray
levels constitutes the image.
Not to be confused with a measurement
matrix.
Image noise
Image quality. Noise in the image is a statistical
fluctuation in signal intensity that does not contribute to the image information. It appears in
the image as a granular, irregular pattern. In principle, the effect is unavoidable and is physically
based.
The noise of the image is a function of the field
strength, coil size (body coil, local coil, array coil)
the pulse sequence used, and the resolution.
Image orientation
–> Slice orientation
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Image quality
The diagnostic quality of an MR image.
Characteristics include:
–> Artifact
–> Contrast (Contrast-to-noise ratio)
–> Noise (Signal-to-noise ratio
–> Resolution
Image reconstruction
system
MR component. Part of the computer system
that reconstructs MR images from the raw data
using a Fourier transformation.
Image resolution
Image quality. Is the ability to differentiate
neighboring tissue structures. The higher the
image resolution, the better small pathologies
may be diagnosed.
Resolution increases with a larger matrix,
smaller FoV, and smaller slice thickness.
–> In-plane resolution
–> Spatial resolution
Image windowing
–> Windowing
Imager
–> Image reconstruction system
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Induction,
electromagnetic
Physics. The electrical voltage in a receiver coil
created by a temporal change in the magnetic
field.
Inflow amplification
Image quality. A blood volume flowing slowly
perpendicular to the slice yields a stronger signal
than the surrounding tissue.
Using a 90° pulse, a bolus is excited within the
slice to be measured. The excited spins cannot
recover fully within a short repetition time. They
remain saturated to a certain extent. The signal is
weaker than that after a sufficiently long repetition time TR in relationship to T1.
However, spin ensembles outside the slice are
fully magnetized. Spins flowing out of the slice
are replaced by fresh inflowing spins. As a result,
vascular magnetization within the slice
increases.
Inflow technique
–> Time-of-flight angiography (ToF)
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Inline Display
Image display. Immediate display of reconstructed images. Frequently used to display
dynamic changes (e.g., CARE bolus and BOLD
imaging).
In-phase image
MR measurement technique. An in-phase
image is generated with a measurement at a
time when two components in the tissue (usually
fat and water) are in the same phase, that is, the
transverse magnetizations have the same orientation and add up. The cause for different phasevelocities is the chemical shift between fat and
water protons.
In-plane resolution
Image quality. In-plane resolution is determined by the size of the pixels. The smaller the
pixel, the better the in-plane resolution.
Integrated Panorama
Array (IPA)
MR components. The concept of the integrated
panorama array (IPA) significantly accelerates
setup time and increases patient throughput.
Depending on the system, up to 4, 8, or 16
independent array coil systems can be connected
IPA:
Integrated Panorama Array
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simultaneously with IPA. Up to 4 CP coil elements
can be combined for a measurement.
Interactive real time
MR measurement technique. Changing measurement parameters in real time.
Interactive shim
Quality assurance. Manual tuning of the shim
coils to improve magnetic field homogeneity.
Shim currents can be set and optimized individually for a selected pulse sequence.
lnterleaved slices
–> Slice sequence
Interpolation
MR measurement technique. Calculation of
values that lie between known values in a mathematical function; e.g., enlarging the image
matrix from 256 × 256 to 512 × 512. The measurement time is not increased, but interpolated
images do require more storage space.
Inversion Recovery
(IR)
MR measurement technique. Method for creating a signal dependent primarily on T1. With
inversion recovery sequences, the longitudinal
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magnetization is inverted in the opposite direction by a 180° pulse. Transverse magnetization
remains equal to zero.
During the subsequent recovery, the negative
longitudinal magnetization decays to zero and
then begins to rise. Because transverse magnetization is not possible, no signal is measured.
To generate an MR signal, the longitudinal
magnetization has to be converted to transverse
magnetization through application of a 90°
pulse.
Inversion time (TI)
Measurement parameters. Interval between a
180° inversion pulse and a 90° excitation pulse in
an inversion recovery sequence.
TI:
Time to Inversion
iPAT
MR measurement technique. iPAT stands for
integrated Parallel Acquisition Techniques. iPAT is
Siemens’ implementation of Parallel Acquisition
Techniques (PAT) on MAGNETOM systems.
iPAT includes the mSENSE and GRAPPA measurement techniques as well as auto-calibration.
iPAT:
integrated Parallel Acquisition
Techniques
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iPAT2
3D imaging. 3D sequences include two phaseencoding directions: the conventional 2D (PE)
direction and the additional phase encoding in
the partitions direction (3D).
The acceleration in the 3D direction is known
as “iPAT2”.
Isocenter
Image quality. The main magnetic field is only
homogeneous within a roughly spherical region
about the isocenter of the magnetic field. In this
area, the examination region are positioned to
ensure the best possible image quality.
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Jet effect
Image quality. Spin dephasing for complex flow
patterns such as turbulences. The degree of signal loss and the size of low-signal regions
depend on the flow patterns and pulse sequence
used. This effect must be taken into account
when evaluating the extent of vascular stenosis.
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k-space
–> Fourier space
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Larmor frequency
MR physics. Frequency at which the nuclear
spins precess about the direction of the outer
magnetic field. The frequency depends on the
type of nuclei and the strength of the magnetic
field.
At 1.0 Tesla, the Larmor frequency of protons is
approx. 42 MHz, at 1.5 Tesla, it is approx.
63 MHz.
–> Precession
Lattice
MR physics. Magnetic and thermal environment
where the nuclei exchange energy during longitudinal relaxation.
Local coils
MR components. Special coils are used for each
area of the body to be examined (surface coil).
They have a high signal-to-noise ratio at a small
measurement field.
Local shim
Quality assurance. The shim is limited to a previously selected local volume.
–> 3D shim
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Localized MIP
MR angiography. Localized “MIPing” improves
image quality and considerably reduces the
reconstruction time. Only a partial data volume is
used which contains the voxels of the vessel of
interest. As a result, the projection includes fewer
background noise pixels and displays less bright
fat signal. Individual vessels can be selected as
well for reconstruction to maintain a comprehensive image.
Localizer
–> Basic image
Logical gradients
MR measurement technique. For orthogonal
slices, each of the 3 physical gradients has
exactly one “logical” task: slice selection,
frequency encoding, and phase encoding. For
oblique slices, the logical gradients are a mix of
the physical gradients.
Longitudinal
magnetization (Mz)
MR physics. Longitudinal magnetization Mz is
the portion of the macroscopic magnetization
vector in the direction of the z-axis, that is, along
the outer magnetic field. After excitation by an
MIP:
Maximum Intensity Projection
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RF pulse, Mz returns to equilibrium M0 with a
characteristic time constant T1.
Mz(t) = M0 (1–exp(–t/T1)
Longitudinal
relaxation
MR physics. Return to equilibrium of the longitudinal magnetization after excitation, due to the
energy exchange between the spins and surrounding lattice (also called spin-lattice relaxation).
Longitudinal
relaxation time
–> T1 constant
LOTA technique
MR measurement technique. Data averaging to
reduce motion artifacts.
LOTA:
Long Term Averaging
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Magnet
–> Permanent magnet
–> Resistive magnet
–> Superconductive magnet
Magnetic field
MR physics. The space surrounding a magnet (or
a conductor with current flowing through it) has
special characteristics. Every magnetic field exercises a force on magnetizable parts aligned along
a primary axis (magnetic north or south pole).
The effect and direction of this force is symbolized by magnetic field lines.
Magnetic field
gradients
–> Gradients
Magnetic field
homogeneity
–> Homogeneity
Magnetic field
strength
MR physics. The strength of the magnetic field
force on magnetizable parts. In physics, the
effect is called magnetic induction. In MR, it is
referred to as magnetic field strength. Units:
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Tesla (T), 1 Tesla is approximately 20,000 times
the strength of the earth's magnetic field.
Magnetic resonance
(MR)
MR physics. Absorption or emission of electromagnetic energy by atomic nuclei in a static
magnetic field, after excitation by electromagnetic RF radiation at resonance frequency.
Magnetic shielding
In space: Shielding
Through tissue: Weakening of the applied magnetic field at the nucleus by the counter field
induced in the electron shell of the surrounding
tissue.
–> Chemical shift
Magnetizability
–> Susceptibility
Magnetization
transfer (MTC)
MR measurement technique. Indirect observation of fast relaxing magnetization through
presaturation. Through magnetization transfer
contrast, the signal from specific “solid” tissue
(e.g., brain parenchyma) is reduced, and the
MTC:
Magnetization Transfer
Contrast
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signal from a more fluid component (e.g., blood)
is retained.
With MTC, the saturation of bound protons is
transferred to adjacent free protons. This reduces
the visible MR signal in these areas.
Magneto-hydro
dynamic effect
Image quality. Additional electrical charges
generated by loaded particles (ions in blood) that
move perpendicular to the magnetic field.
Magnitude contrast
angiography
MR application. Used to display slow flow with
good resolution across a large volume.
Two data volumes are measured: the flow
rephased image shows bright flow, and the flow
dephased image shows dark flow. Stationary tissue looks the same in both data volumes. The
data volumes are subtracted from one another
pixel-by-pixel. What remains is the signal intensity of the flowing blood.
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Magnitude image
Image reconstruction. Normal image display.
In a magnitude image, the gray value of a pixel
corresponds to the magnitude of the MR signal
at that location.
Alternative: Phase images
MAP shim
Quality assurance. MAP shim globally tunes the
shim currents. Correction functions are calculated using a fixed algorithm and applied to the
corresponding shim currents. As can be seen, the
shim is applied to the entire measurement field.
Modern systems no longer require the MAP
shim.
Matrix
–> Image matrix
–> Raw data matrix
Matrix coils
MR components. Matrix coils have multiple coil
elements combined into groups (clusters), typically 3 coil elements per cluster. Each coil element is equipped with a low-noise preamplifier
to maximize the signal-to-noise ratio. For exam-
MAP:
Multi-angle projection
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ple, a spine matrix coil has 24 coil elements and
24 preamplifiers.
Matrix coil mode
Measurement parameters. The Matrix coil
mode defines the allocation between Matrix coil
elements and the RF receive channels.
• Matrix coil mode CP
• The coil elements of a coil cluster are combined
to one RF receive channel. This mode is optimized for a maximum signal-to-noise ratio.
Example: In the Matrix coil mode CP, the head
matrix coil acts like a CP head array with 4 elements.
• Matrix coil mode Dual or Triple
The coil elements of a coil cluster are allocated
to two or three RF receive channels. This allows
for additional information that may be used for
improving the signal-to-noise ratio at the image
margin and/or for obtaining higher PAT factors.
Example: In the Matrix coil mode Triple, the head
matrix coil acts like a CP head array with 12 elements.
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Matrix size
Measurement parameters. Size of the raw data
matrix; influences not only the measurement
time, but also the resolution and signal-to-noise
ratio.
With a square raw data matrix, the number of
rows equals the number of columns.
Maximum Intensity
Projection
–> MIP
MDDW
Diffusion imaging. To compute the diffusion
tensor, the technique provides multi-directional
diffusion weighting (MDDW) measurements in at
least 6 spatial directions. One diffusion-weighted
image each is generated per slice position,
b-value, and direction of diffusion (for b > 0).
Measurement field
MR physics. Spherical volume in the center of
the magnetic field where the field has a defined
homogeneity. For MR examinations, objects to
be measured have to be positioned at all times in
the measurement field (to prevent signal distortions).
MDDW:
Multi Directional Diffusion
Weighting
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Measurement matrix
Raw data matrix, not to be confused with the
image matrix.
Measurement
sequence
–> Pulse sequence
Measurement time
MR measurement technique. The measurement time for a 2D measurement is as follows:
Measurement time = no. of scans x TR x no. of
acquisitions
MEDIC technique
MR measurement technique. Multiple echoes
acquired in one measurement are combined into
an image. The advantage: higher SNR per time
period, fewer artifacts. Application: cervical
spine, joints.
MIP
Post-processing. Maximum projections can be
reconstructed from 3D or multi-slice measurements that can be combined into MIP series. This
procedure is used mainly for MR angiography.
Blood vessels are displayed brighter than the rest
of the image.
MEDIC:
Multi-Echo Data-Image
Combination
MIP:
Maximum Intensity Projection
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Mosaic image
BOLD imaging. Between16 to 64 EPI images are
compiled into a mosaic image. This increases the
clarity of BOLD displays.
Motion artifact
Image quality. Results from random or involuntary movement: breathing, heartbeat, blood
flow, eye movement, swallowing, and patient
movement. The effect appears as ghosting or
smearing in the images. In the phase-encoding
direction only.
MPR
–> Multi-planar reconstruction (MPR)
MPRAGE technique
MR measurement technique. MPRAGE is a
3D extension of the TurboFLASH technique with
prepared inversion pulses. Only one segment or
partition of a 3D data record is obtained per preparatory pulse.
After the acquisition, all rows within a 3D partition use delay time TD. The delay time is necessary to prevent saturation effects.
MPRAGE:
Magnetization Prepared Rapid
Gradient Echo Imaging
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MR angiography
MR application. Angiography with MR does not
really display the blood volume, but rather a specific physical characteristic of the blood; for
example, the magnetization status or local velocity. This is perceived as blood volume. MRA does
not display a single vessel, but rather all vessels
in the blood volume. Various views can be subsequently reconstructed (MIP) from 3D data volumes.
MR cardiology
MR application. The advantages of cardiac MR
include:
• free selection of image planes and FoVs
• high tissue contrast
• temporal and spatial resolution
Image plane projections can be compared in
angiocardiography, scintigraphy, or
2D echocardiography. Multiple cardiac slices can
be acquired along the respective slice plane. In
this way, complete anatomical display of the
heart in all three dimensions is provided. Data
records acquired across cardiac phases enable
cine display of the heartbeat.
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Subsequent quantitative evaluation of cardiac
studies enables the following:
• Manual or semi-automatic segmentation of the
inner and outer cardiac walls of the left ventricle, and the inner wall of the right ventricle: ED
and ES images or the complete cardiac cycle.
• Calculation of ventricular volume, myocardial
mass, and functional parameters
• Evaluation of myocardial wall thickness;
changes in wall thickness (between the ED and
ES phase or during the cardiac cycle) are evaluated for each sector
• Viability, perfusion, coronary angio
MR contrast agent
–> Contrast agent
MR images
The MR image consists of a multitude of image
elements, also known as pixels. Pixels are allocated to a matrix in a checkered pattern. Every
pixel in the image matrix displays a specific gray
scale. Viewed as a whole, this gray scale matrix
provides the image.
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The gray scale of a pixel mirrors the measured
signal intensity of the corresponding volume element (voxel). In turn, the signal intensity of a
voxel depends on the respective transverse magnetization.
MR imaging
Images of objects, for example, the human body,
are displayed with magnetic resonance using
magnetic gradient fields. In practical application,
the distribution of protons in the body is displayed.
The clinically relevant objective of MR imaging
is the differentiation between pathological and
healthy tissue (image contrast).
MR sensitivity
MR physics. Atomic nuclei for MR examinations
have to be “MR sensitive”; that is, they must have
a nuclear spin. This condition excludes all atomic
nuclei with an even number of protons and neutrons.
Since the hydrogen isotope 1H is the most sensitive, it is used as a reference in relationship to
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other atom nuclei. Its relative sensitivity is 1 or
100 %.
MR signal
MR physics. Electromagnetic signal in the
RF range. Caused by the precession of transverse
magnetization created by a variable voltage in a
receiver coil (dynamo principle). The temporal
progression of this voltage is the MR signal.
MR spectroscopy
(MRS)
MR application. MR spectroscopy provides the
non-invasive measurement of cellular metabolic
relationships. An MR spectrum shows the dependence of the signal intensity on the chemical
shift for a measurement volume (voxel). The concentration of metabolites contributing to the
spectrum can then be inferred.
In MR spectroscopy, the MR signal is measured
as a function of time: a rapidly decreasing highfrequency oscillation. Using a Fourier transformation, the oscillation is converted into a display
of its frequency component, the spectrum.
In the area of intermediary metabolism,
MR spectroscopy is an important method for in-
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vitro and in-vivo examination of tissue and
organs.
mSENSE
MR measurement technique. Further development of SENSE with auto-calibration and a modified algorithm for image reconstruction.
mSENSE:
Modified Sensitivity Encoding
MTT image
Perfusion imaging. An MTT image can be reconstructed for an image displayed. It displays the
mean transit time of the contrast agent bolus
and enables hemodynamic interferences to be
evaluated.
MTT:
Mean Transit Time
Multi-directional
diffusion weighting
–> MDDW
Multi-echo sequences
MR measurement technique. Pulse sequence
that excites multiple echoes with different
degrees of T2 weighting. Signal height reduces
with transverse relaxation. This drop in signal can
be used to calculate a pure T2 image.
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Multi-level MRA
MR angiography. For peripheral or whole-body
angiography, the multi-level principle (also:
Multi-step Angio) simplifies the measurement
and reduces the measurement time. The area to
be examined is measured at individual sections
(levels), during automatic table feed. The data
obtained are subsequently combined into an
overall image.
Multi-planar
reconstruction (MPR)
Post-processing. Enables new images of any
orientation to be reconstructed based on a 3D or
gapless multi-slice measurement.
Multi-slice imaging
MR measurement technique. Variant of
sequential imaging. The recovery period of the
first slice excited is used to measure additional
slices (time-savings). The slices are interleaved.
Multi-step angio
–> Multi-level MRA
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Multi-venc sequence
Phase-contrast angiography, A sequence that is
equally sensitive to various flow velocities. Used
to acquire wide variations in flow velocity, e.g.,
in the peripheral arteries.
venc:
velocity encoding
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NATIVE
MR angiography. Images of arteries and veins
without contrast agent (native).
• NATIVE SPACE: for peripheral MRA; based on a
fast 3D TSE sequence; image data are computed via inline subtraction of two ECG-triggered
data records (systole and diastole).
NATIVE TrueFISP: for thoracic-abdominal MRA
(e.g., renal arteries). The intrinsic contrast is generated by the inflow of blood with non-saturated
spins into a presaturated volume.
Native image
Contrast agent study. MR image without the
use of contrast agent, for example as a pre-contrast study.
BOLD imaging. Non-activated image (baseline).
Navigator echo
MR measurement technique. Additional spin or
gradient echoes for detecting changes in object
position in a measurement volume, or other
changes. Suitable for use with interventional procedures or respiratory gating.
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Neuro imaging
MR application. General term for brain and nervous system applications, such as BOLD imaging.
Noise
–> Image noise
Non-selective pulse
MR measurement technique. When data are
acquired with a non-selective pulse, a longer TR
is required for multi-slice measurements or
repeated measurements of the same slice. The
longer TR is required to ensure that magnetization between consecutive measurement recovers
sufficiently and that the individual measurements do not interfere with one another.
Use with 3D volume measurements and presaturation techniques (e.g., magnetization transfer).
Normalization filter
Image quality. Equalizes signal intensity when
using surface coils. Using the filter, the signal
intensity of areas close to the coil is reduced; the
signal intensity is increased in areas farther from
the coil.
Used primarily with array coils.
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Nuclear spin
MR physics. Atomic nuclei with an odd number
of neutrons and protons have what is called
nuclear spin. For MR imaging, only hydrogen protons are used. For MR spectroscopy, other nuclei
are used, such as phosphor, fluorine, and carbon.
Number of partitions
–> Partitions
Number of slices
Measurement parameters. Multiple slices are
usually acquired during an MR measurement.
The maximum number of slices of a pulse
sequence or measurement protocol depends on
the repetition time TR.
–> Multi-slice imaging
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Oblique slice
Measurement parameters. Obtained by rotating an orthogonal slice (sagittal, coronal, or
transverse) about a coordinate axis in the image
plane.
Off-center
(Eccentricity)
Slice positioning. Shifting the center of a slice
group from the center of the magnetic field
within the slice plane.
Opposed-phase
image
MR measurement technique. An opposedphase image is acquired at a time when two
components in the tissue (usually fat and water)
have opposite phases, that is, the transverse
magnetizations of the two components have
opposite orientations and partially cancel one
another. Cause for the difference in phase is a
chemical shift between fat and water protons.
Orthogonal slices
Slice positioning. Slices oriented perpendicular
to one another. Three basic orientations are
available: sagittal, coronal, and transverse (axial)
–> Slice orientation
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Out-of-phase
–> Phase cancellation
Overlap
–> Aliasing artifact
Oversampling
Measurement parameters. Method for preventing aliasing artifacts.
Readout oversampling: Doubling the sampling
points in the frequency-encoding direction without prolonging the measurement time. The additional part is discarded after reconstruction.
Phase oversampling: Measurement data acquisition beyond the FoV in the phase-encoding
direction. Increases the SNR. The measurement
time increases accordingly. 100 % phase oversampling has the same effect as double the number of acquisitions.
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PACE
MR measurement technique. During the measurement, PACE corrects respiratory and motion
artifacts in real time by reducing the offset
between the slices. This allows for, e.g., multiple
breathhold examinations a well as free breathing
during a measurement.
–> 1D PACE
–> 2D PACE
–> 3D PACE
Paradigm
BOLD imaging. Planned sequence of the
functional measurement, for example: 10 nonactivated images (baseline), 10 active images,
2 ignored images.
Parallel acquisition
techniques
–> PAT
Parallel imaging
–> PAT
Parallel saturation
Slice positioning. By saturating areas parallel to
the slice plane but outside the slice of interest,
blood flowing to the measurement area pro-
PACE:
Prospective Acquisition
Correction
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duces almost no signal at the beginning of the
measurement. This eliminates the vascular
intraluminal signal, and prevents ghosting in the
phase-encoding direction.
This presaturation can be performed on both
sides of the slice. Parallel saturation slices shift
with the slices of interest, simplifying planning.
Parametric map
Post-processing. Parametric maps display the
T1, T2, or T2* characteristics of the acquired tissue, enabling, e.g., early detection of arthritis in
osteology.
Diffusion imaging. Parametric maps in diffusion
imaging are created by measuring the diffusion
tensor. They are used to, e.g., display anisotropic
diffusion characteristics of the brain. Example:
FA map.
Perfusion imaging. To display interferences in
perfusion. Example: Time-to-Peak map (TTP).
Partial-Fourier
MR measurement technique. To reduce the
phase-encoding steps during the measurement
so that the raw data matrix is filled with fewer
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rows. Allows for shorter echo times. Special case:
Half-Fourier matrix
Partial Parallel
Acquisition (PPA)
–> PAT
Partitions
3D imaging. During 3D imaging, entire volumes
and not just individual slices are stimulated. A
3D slab comprises multiple gapless partitions
The number of partitions corresponds to the
number of slices during 2D imaging.
Partition thickness
3D imaging. The effective slice thickness of individual partitions in a 3D slab is the slab thickness
divided by the number of partitions.
Passive shielding
MR components. Older magnets were clad in
soft iron that acted as flux return and significantly reduced the stray field. The overall weight
of the system was drastically increased.
Today, active shielding is the preferred method.
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PAT
MR measurement technique. PAT is the generic
term for parallel imaging techniques. Other
terms for PAT include “Parallel Imaging and
Partial Parallel Acquisition”.
Two groups of PAT are differentiated: with the
image-based methods (e.g., SENSE, mSENSE),
the PAT reconstruction is performed following
the Fourier transformation. With the k-spacebased methods (e.g., SMASH, GRAPPA), the PAT
reconstruction is performed prior to the Fourier
transformation.
PAT shortens the measurement time without
degrading image resolution. The lower number
of measurement lines reduces the signal-tonoise.
A prerequisite for PAT is the use of array coils as
well as the calculation of the coil profile of all
array coil elements (e.g., via auto-calibration).
The most important advantages of PAT: shorter
breathhold times, higher temporal resolution of
dynamic measurements and sharper images with
echo-planar imaging (by reducing the echo
train).
PAT:
Parallel acquisition techniques
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–> iPAT
–> iPAT2
PAT factor
Measurement parameters. The PAT factor is a
measure of the phase-encoding steps reduced
through PAT. Example: for a PAT factor of 2, each
second step is skipped. This cuts the measurement time in half.
For iPAT2, the PAT factor is the product of the
two PAT factors in the phase-encoding and the
partitions direction. Example: a PAT factor of 12
comprises a PAT factor of 4 in the phase-encoding direction and a PAT factor of 3 in the partitions direction.
PBP image
–> Percentage of baseline at peak
PC Angio
–> Phase-contrast angiography
Peak
MR spectroscopy. Theoretically, the frequency
display of a pure sine wave is a single spectral
line at the point of the resonance frequency. In
reality, the spectral line spreads into a blurred
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peak. The cause are the spin-spin effects and the
field inhomogeneity (magnet and patient).
Peak characteristics: resonance frequency (ν0),
peak height (h) peak width at half height (b) (Full
Width Half Maximum FWHM), area.
Percentage of
Baseline at Peak
(PBP)
Perfusion imaging. A percentage of baseline at
peak image can be reconstructed for the slice.
The gray scale displays the signal change relative
to a basic image prior to administering contrast
agent.
Perfusion imaging
MR application. Technique for evaluating organs
and organ areas used frequently together with
contrast agent. Areas poorly supplied with blood
display a signal change over time. Examples:
T1-sensitive perfusion of liver or sella lesions.
T2*-sensitive perfusion of a stroke. Frequently
used with EPI sequences.
Perfusion can be displayed without a contrast
agent by using inversion recovery.
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Peripheral
angiography
MR application. MR angiography of the peripheral vascular system; has special requirements:
• arterial flow is often pulsating
• large volumes have to be measured
• images must clearly distinguish between arteries and veins
Most often, 3D gradient echo protocols with
contrast agent are being used. Measurements
are performed with tabletop movement in several stages. They require an optimized timing
sequence.
Permanent magnet
MR components. Permanent magnets consist of
large blocks of magnetic material, usually horseshoe-shaped. They have a permanent magnetic
field. As a result, they do not need to be supplied
with energy or cooling (maximum field strength
0.3 Tesla).
Phantom
Quality assurance. Synthetic item with known
dimensions and measurement characteristics.
Usually a container filled with fluid and a built-in
plastic structure of various sizes and shapes.
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Phantoms are used to test the system and the
quality features of imaging systems.
Phase cancellation
(chemical shift)
Image quality. Fat and water protons have only
slightly different resonance frequencies. This
results in phase cycling. After an excitation pulse,
the fat and water spins of a 1.0 Tesla magnet are
alternatively in and out-of-phase every 3.4 ms.
For this reason, the signal intensity of a voxel
containing fat and water oscillates with an
increasing echo time. The strength of the oscillation depends on the relative proportion of fat
and water protons in the tissue. This effect
occurs only with gradient echo sequences.
Phase-contrast
angiography (PCA)
MR application. Method for displaying vascular
flow. With PCA, the phase change of the spins in
flowing blood induced by velocity is used to distinguish the blood from stationary tissue. Only
flowing spins contribute to the signal. The blood
contrast in the image is proportional to the local
flow velocity.
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2D and 3D PCA protocols have established flow
sensitivity for all three spatial directions. This
allows the display of various flow velocities.
Applications: slow flow, “bent” vessels with
variable flow direction, overview projection
images.
This technique is also the basis for flow measurements.
Phase encoding
MR measurement technique. Method for defining the rows in the measurement matrix.
Between the RF excitation pulse and the
MR readout signal, a magnetic field gradient is
switched briefly, applying a phase shift to the
spins from row to row. Phase-encoding steps are
required to fully scan the slice depending on the
matrix (e.g., 256 or 512). The subsequent Fourier transformation allocates the various phasings to the respective rows.
Phase-encoding
gradient
MR measurement technique. Magnetic field
gradient switched in the phase-encoding direction.
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Phase-encoding step
MR measurement technique. Phase encoding
of an MR image requires that there are as many
excitations and signal acquisitions as there are
image matrix rows (e.g., 256 or 512). The amplitude of the phase-encoding gradient changes
incrementally from excitation to excitation. For
this reason, each row of raw data has different
phase information.
Phase images
Image reconstruction. In addition to regular
magnitude images, phase images can also be
reconstructed from the raw data measured.
In a magnitude image, the gray scale of a pixel
corresponds to the magnitude of the MR signal at
that location. In the phase image, each pixel gray
scale represents the respective phasing between
−180° and +180°.
Spin ensembles can be distinguished from stationary tissue in phase images. Stationary spins
have the same phasing, moving spins have differing phasing depending on their velocity.
Phase oversampling
–> Oversampling
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Phase shift
MR physics. Loss of phase coherence in precessing spins (signal reduction). In most physiological situations, vascular spins move at variable
velocities. Faster flowing spins are subject to a
stronger phase shift than slower flowing spins.
Physical gradients
–> Gradient coils
Physiologically
controlled imaging
MR measurement technique. Physiological
movements such as the heartbeat, breathing,
blood flow, or fluids generally cause artifacts that
make an accurate interpretation of an MR image
difficult, if not impossible. Physiologically-controlled imaging suppresses these artifacts.
–> Cardiac triggering (ECG triggering, pulse
triggering), respiratory triggering
Pixel
Image quality. Smallest picture element of a digital image. To display the MR image, every pixel
in the image matrix contains a specific gray
scale.
Pixel size = FoV / matrix size
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Precession
MR physics. Gyration of the rotation axis of a
spinning body about another line intersecting it
so as to describe a cone.
Precession frequency
–> Larmor frequency
Presaturation
Image quality. Regional presaturation,
frequency-selective presaturation (fat saturation,
water saturation) presaturation with inversion
pulses (e.g., Dark Blood techniques).
Regional presaturation can be used to reduce
the signal from unwanted tissue. For example, to
minimize artifacts caused by movement of the
thorax. An additional saturation pulse is applied
at the beginning of the pulse sequence to saturate the spins within the saturation slice.
The saturated region produces almost no signal
and appears black in the image.
Proton density
MR physics. Number of hydrogen protons per
unit of volume (generally: spin density).
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Proton density
weighting
Image quality. In a proton density-weighted
MR image, contrast is affected primarily by the
proton density of the tissue to be displayed.
Pseudo gating
Physiologically-controlled imaging. Pseudo
gating is obtained with a TR corresponding to the
RR interval in the cardiac cycle. This application is
not intended for cardiac imaging but rather for
the prevention of flow artifacts (assuming a stable heart rate).
PSIF sequence
MR measurement technique. The PSIF
sequence is a time-inverted FISP sequence. It
produces a strong T2-weighted contrast in a
short measurement time.
Pulse sequence
MR measurement technique. Temporal
sequence of RF pulse and gradient pulse to excite
the volume to be measured, generate the signal,
and provide spatial encoding. Each pulse
sequence requires a repetition time TR optimized
for the respective contrast.
PSIF:
FISP read backward
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Typical pulse sequences: spin echo, gradient
echo, TurboSE, Inversion Recovery, EPI, etc.
Pulse triggering
Physiological imaging. Pulse triggering suppresses motion and flow artifacts, as a result of
pulsating blood and fluid. The pulse wave
obtained with, e.g., a finger sensor is used as the
trigger.
Although pulse sensors are easier to apply than
ECG electrodes, they are less accurate and not
suitable for cardiac imaging.
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Quadrature coil
–> CP coil
Quality assurance
Method for tuning the components and parameters of an MR system, for determining spatial resolution, contrast resolution, signal-to-noise
ratio, and other quality-relevant parameters.
Quench
Super-conductive magnet. Sudden loss of
superconductivity of a magnet coil due to a local
temperature increase in the magnet. The
cryogen used for superconductivity evaporates
rapidly, quickly reducing the magnetic field
strength.
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RADIANT
MR mammography. 3D reconstruction similar
to ultrasound for breast imaging, generates a
360° view with the nipple as the center.
Radio frequency (RF)
MR physics. Frequency required to excite hydrogen nuclei to resonate. For MR, frequencies in
the Megahertz range (MHz) are used, e.g.,
63 MHz at 1.5 Tesla. The primary effect of RF
magnetic fields on the human body is energy dissipation in the form of heat, usually on the surface of the body. Energy absorption is an important value for establishing safety thresholds.
–> Specific absorption rate (SAR)
RARE technique
MR measurement technique. Fastest Turbo
spin-echo technique where a complete echo
train of 256 or more echoes is read out after a
single excitation pulse. (Single-shot technique
TurboSE). Each echo is individually phaseencoded.
Raw data
MR measurement technique. The MR measurement does not directly obtain the image. Instead
RARE:
Rapid Acquisition with
Relaxation Enhancement
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raw data are generated that are subsequently
reconstructed into an image.
Raw data filter
Measurement parameters. Raw data can be filtered prior to image reconstruction. The Hanning
filter is provided with various weightings. The filter is able to reduce edge oscillations, for example.
Raw data matrix
MR measurement technique. As with a hologram, every point in the raw data matrix contains
part of the information for the complete image.
This is why a point in the raw data matrix does
not correspond to a point in the image matrix.
The rows arranged about the center of the raw
data matrix determine the basic structure and
contrast in the image. The outer rows of the raw
data matrix provide information regarding the
borders and contours of the image, detailed
structures, and also determine the resolution.
Using the two-dimensional Fourier transformation, the raw data matrix is converted into the
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image matrix. For this reason, raw data rows are
also referred to as Fourier lines.
Readout
–> Readout direction
Readout bandwidth
Measurement parameters. A pulse sequence's
received bandwidth in the readout direction.
Readout direction
MR measurement technique. The direction in
which the MR signal is read out. It corresponds to
the direction of frequency encoding.
Receiver bandwidth
–> Readout bandwidth
Receiver tuning
MR measurement technique. Setting of the
receiver dynamic of the analog-to-digital
converter (ADC). This is not necessary for many
modern systems with large receiver dynamic
ranges.
Rectangular FoV
RecFoV
Measurement parameters. When the object of
interest is oval, a rectangular field of view can be
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selected. This applies in particular to examinations of the abdominal and spinal regions.
The rectangular FoV can be combined with a
reduced measurement matrix. For example, a
rectangular FoV is sampled with an adjusted
matrix. A rectangular image is obtained with less
rows than columns.
The full resolution raw data space is sampled
less densely, so resolution is not lost. Measurement time is reduced, but so is the signal-tonoise ratio.
Reduced matrix
Measurement parameters. When you select
fewer lines than columns for the measurement
matrix, a reduced matrix results. The high local
frequencies are no longer measured. This
reduces the measurement time. The lines not
measured are filled with zeroes prior to image
reconstruction (zero filling). This corresponds to
an interpolation in the phase-encoding direction;
therefore, a square image is still displayed on
screen.
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Reference image
Post-processing. Selected template for defining
reconstruction methods, such as MIP or MPR.
Refocussing
–> Rephasing
Region of Interest
(RoI)
Post-processing. An RoI is the area in the
MR image singled out for evaluation.
Registration
Measurement preparation: Prior to an
MR examination, each patient has to be registered. The patient data are entered, providing for
a clear allocation between the patient and
MR image.
Interventional imaging: Link between the “real”
position and the measured data record.
Matching data from different modalities.
Relaxation
MR physics. Dynamic, physical process where a
system returns from a state of imbalance to equilibrium.
–> Longitudinal relaxation
–> Transverse relaxation
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Relief artifact
Image quality. Relief-like structures along the
transitions between tissue with significant differences in fat and water content (e.g., spleen, kidneys, eye sockets, spine, and spinal disks).
The cause is a chemical shift: the signals of the
fat and water protons in a voxel are allocated to
different image pixels during image reconstruction. At transitions of fat and water, these incorrect encodings lead to a higher signal (dark surface area) or to an invalid signal (bright areas) in
the respective frequency-encoding direction.
Repetition time (TR)
Measurement parameters. In general, the time
between two excitation pulses. Within the TR
interval, signals may be acquired with one or
more echo times, or one or more phase encodings (depending on the measurement technique). TR is one of the measurement parameters that determines contrast. The acquisition
time (TA) is directly proportional to TR.
Rephased-Dephased
–> Magnitude contrast angiography
TR:
Time to Repetition
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Rephasing
MR physics. Reversal from dephasing; the spins
go back into phase. Obtained through a 180°
pulse that creates a spin echo, or a gradient pulse
in the opposite direction.
Resistive magnet
MR components. Resistive magnet. A magnet
whose magnetic field is generated using a normally conductive coil system. When used with
copper or aluminum conductors, this system creates a maximum field strength of 0.3 Tesla. Disadvantage: high electric costs.
Resolution
–> Image resolution
Resonance
Physics. Exchange of energy between two systems at a specific frequency. In musical instruments, for example, strings at the same pitch will
resonate.
Resonance frequency
MR physics. The frequency at which resonance
occurs. In MR, this frequency is used for the
RF pulse that affects the spin equilibrium, that is,
it matches the Larmor frequency.
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Respiratory gating
Cardiac imaging. Synchronization of measurement with the patient's breathing. Diaphragm
movement is detected with the navigator echo.
Respiratory triggering
Physiologically-controlled imaging. Technique
for reducing respiratory artifacts. Data acquisition is synchronized to breathing. A respiratory
signal acquired with suitable sensors or MR
methods (navigator echo) is used as the trigger
signal.
Restore sequence
MR measurement technique. The Restore
sequence in T2-weighted TurboSE imaging
increases the signal of substances with long
relaxation times (e.g., CSF). This is realized via
the use of a 90° RF pulse (so-called “Restore
pulse”) at the end of the echo train of the
TurboSE sequence. This rotates the transverse
magnetization back in the longitudinal axis,
accelerating relaxation of the longitudinal magnetization. It allows for a shorter TR with comparable contrast as well as a reduced measurement
time.
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Retrospective gating
Cardiac imaging. Simultaneous acquisition of
untriggered data and the ECG signal. The ECG
signal is used during subsequent post-processing
to assign the images to the correct phase in the
cardiac cycle.
May also be used for pulsatile flow.
REVEAL
Diffusion imaging. Diffusion-weighted singleshot technique for differential diagnosis when
evaluating lesions in the overall body, especially
in the torso.
RF antenna
–> RF coils
RF coils
MR components. Antennas, called coils in the
language of MR, are used to send RF pulses and/
or receive MR signals.
As transmitter coils, they should excite the
nuclei in the volume of interest as homogeneously as possible: All nuclei should receive the
same excitation.
As receiver coils, they should receive the
MR signal with as little noise as possible. The sig-
RF:
Radio frequency
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nal strength depends on the volume of excitation
in the coil and the distance to the object to be
measured. The noise, however, depends primarily on the size of the coil.
RF pulse
–> Excitation pulse
RF shielding
Image quality. The radio-frequency pulses used
in MR is in the radio frequency range. They have
to be shielded for two reasons:
• external electromagnetic waves (e.g., radios,
electrical machines) would distort the measurement and generate image artifacts
• to avoid interference with other receivers, the
RF signals of the system should not extend beyond the system
RF shielding is provided by installing the magnet and receiver coils in a Faraday cage (a space
that cannot be penetrated by high-frequency
waves). For that purpose, the magnet room is,
e.g., shielded with copper and windows are covered with electrically-conductive screens.
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RF spoiling
–> Spoiler gradient
RF tuning
MR measurement technique. Adjustment of
components prior to the measurement, usually
automatic.
–> Frequency tuning
–> Receiver tuning
–> Transmitter tuning
Rise time
MR measurement technique. The time required
by the gradient field to rise from zero to the maximum value.
Rows
MR measurement technique. The phaseencoded portion of the measurement matrix.
Frequently, just a row in the image is displayed.
–> Columns
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Sagittal
–> Orthogonal slices
Saturation
MR physics. The state in which spins have no net
longitudinal or transverse magnetization. It is not
possible to obtain an MR signal from saturated
tissue.
Saturation recovery
(SR)
MR measurement technique. Technique for
generating primarily T1-dependent contrast
through a series of 90° excitation pulses. Immediately after the first pulse, longitudinal magnetization is zero because the tissue is saturated. The
next 90° pulse is not applied until longitudinal
magnetization has partially recovered (recovery).
The recovery time depends on the T1 constant
of the tissue.
Saturation slice
Slice positioning. Regional presaturation to suppress undesired signals for specific areas, either
within the slice or parallel to it.
–> Parallel saturation
–> Presaturation
–> Traveling sat
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Scan
1. Acquiring one or several MR signals after a single excitation pulse
2. Acquiring a complete raw data record
Scan time
–> Measurement time
Scout
–> Basic image
SE-CSI technique
MR spectroscopy. Hybrid procedure based on
the spin-echo SVS technique.
Segmented HASTE
MR measurement technique. Variant of the
standard HASTE technique. With segmented
HASTE, half the image information is acquired
after the first excitation pulse, and the other half
after the second excitation pulse. The raw data,
acquired after the first and second excitation
pulse, are then interleaved into the raw data
matrix. A long repetition time TR is selected to
allow the spin system to recover between excitation pulses. Any dead time can be used to excite
additional slices.
SE-CSI:
Spin-Echo Chemical Shift
Imaging
HASTE:
Half-Fourier Acquisition
Single-Shot TurboSE
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Advantage: The length of the multi-echo pulse
train is cut in half. HASTE sequences may also be
divided into more than 2 segments.
Selective excitation
MR measurement technique. Limits excitation
to the region selected. Magnetic field gradients
are combined with a narrow band RF pulse.
Selective excitation is also used with fat and
water suppression. Low band RF pulses excite
protons bound in fat or water.
SENSE
MR measurement technique. Image-based parallel acquisition technique (PAT). With SENSE,
PAT reconstruction is performed after the Fourier
transformation.
Sensitivity
–> MR sensitivity
Sequence
–> Pulse sequence
Sequential
multi-slice imaging
MR measurement technique. The slices in the
area under examination are measured sequen-
SENSE:
Sensitivity Encoding
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tially. The slices requested are selected using
suitable gradients (selective excitation).
Shielding
–>
–>
–>
–>
Active shielding
Magnetic shielding
Passive shielding
RF shielding
Shim
Quality assurance. Correction of magnetic field
inhomogeneities caused by the magnet itself,
ferromagnetic objects, or the patient's body. The
basic shim usually involves the introduction of
small iron pieces in the magnet. The patientrelated fine shim is software-controlled and performed using a shim coil.
–> Active shim
–> Global Shim
–> Interactive shim
–> Local shim
–> 3D shim
Shim coils
MR components. Coils that create weak additional magnetic fields in various spatial direc-
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tions. Used to correct inhomogeneity in the main
magnetic field.
Signal
–> MR signal
Signal elimination
Image quality. Areas in the image that do not
generate a signal, that is, they are black. There
are different reasons for signal elimination: Metal
artifacts, susceptibility artifacts, flow effects, and
saturation effects. Flow effects may occur with
fast flow when using spin-echo sequences. After
half the echo time, the bolus has flown out of
the slice completely. Since it is no longer
acquired by the slice selective 180° pulse, it no
longer produces a spin echo: blood appears black
in the image.
Signal-to-noise ratio
(SNR)
Image quality. Relationship between the intensity of signal and noise. Ways to improve SNR
include:
• increasing the number of averages
• increasing the measurement volume (although spatial resolution degrades)
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• using special coils and local coils
• smaller bandwidth
• shorter echo time
• thicker slice
Simultaneous
excitations
MR measurement technique. Special averaging procedure that excites two slices simultaneously. This enables, e.g., more slices to be
acquired in the same measurement time.
A simultaneous excitation offers the following
advantages:
• shorter TR with the same number of slices, the
same measurement time, and the same number of concatenations
• double the number of slices with the same
signal-to-noise ratio at the same TR and acquisition time
Single-shot technique
MR measurement technique. All image information is acquired in a single pulse. The magnetization of a fully relaxed spin system is used.
Each of the subsequent echoes is given a different phase encoding. Only slightly more than half
A B C D E F G H I J K L M N O P Q R S T U V W Z 123
the raw data are acquired. The image is obtained
through Half-Fourier matrix reconstruction.
Single-shot techniques include: EPI, RARE,
HASTE.
Single volume
spectroscopy
MR spectroscopy. SVS methods map the metabolic information from the Volume of Interest
(VoI) in a spectrum. Single volume techniques
are advantageous in case of pathological
changes that cannot be spatially limited to a few
VoIs: to a large extent, local magnetic field inhomogeneities can be compensated for with a
“local volume-sensitive shim”.
Currently, clinical 1H spectroscopy uses single
volume techniques based on spin echoes (SE) or
stimulated echoes (STEAM).
Slab thickness
3D imaging. The slice thickness of a 3D slab.
Slew rate
MR measurement technique. Gradient field
increase by unit time (unit: T/m/s)
Slew rate = gradient strength/rise time
SVS:
Single Volume Spectroscopy
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Slice
Measurement parameters. Thin, three-dimensional cuboid uniquely defined by slice position,
FoV, and slice thickness The center plane of the
slice is the image plane.
Slice boundary artifact
Image quality. Slice boundary artifacts are
caused through signal loss at the boundaries
between slices (Slab Boundary Artifact, Venetian
Blind Artifact). They appear typically during conventional 3D multi-slab measurements and lead
to oscillations in signal intensity and staircase
phenomena along the vessels.
Slice distance
Measurement parameters. The separation
between the center planes of two sequential
slices or 3D slabs.
Slice gap
Measurement parameters. The gap between
the nearest edges of two adjacent slices. Not to
be confused with slice distance.
Slice orientation
Measurement parameters. Orthogonal planes
are available for use as the basic slice orientation:
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• sagittal
• coronal
• transverse
An oblique or double-oblique slice is obtained
by rotating the slice out of the basic orientation.
Slice position
Measurement parameters. The position of the
slice to be measured within the area under examination.
Slice positioning
Graphical positioning of the slices/saturation
regions to be acquired in a basic image.
Slice selection
MR measurement technique. To display an
MR image of the human body, the slice desired
has to be selectively excited. For orthogonal
slices, a magnetic field gradient is applied perpendicular to the desired slice plane (slice-selection gradient). Oblique and double-oblique slices
are excited by simultaneously applying 2 or 3
gradient fields.
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Slice sequence
Measurement parameters. For multi-slice measurements, the excitation sequence can be
selected as needed:
• ascending (1, 2, 3, ..., n)
• descending (n, n−1, ..., 3, 2, 1)
• interleaved (1, 3, 5, ..., 2, 4, 6, ...)
• freely defined
Slice shift
Measurement parameters. Distance between
the center of a slice group and the center of the
magnetic field in the slice-selection direction.
Slice thickness
Measurement parameters. The thickness set for
the slice to be measured. The thicker the slice,
the stronger the signal and the better the signalto-noise ratio. However, spatial resolution drops.
SMASH
MR measurement technique. k-space-based
method of Parallel Acquisition Technique (PAT)
With SMASH, PAT reconstruction is performed
prior to the Fourier transformation.
SMASH:
Simultaneous Acquisition of
Spatial Harmonics
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Smearing artifact
Image quality. In the case of non-periodic movements, such as eye movement, the excited spins
may be at a different location in the gradient
field at the time of the echo. This results in incorrect phase encoding. This smears the object in
the phase-encoding direction. These artifacts are
more discrete for periodic movements (respiration, blood flow).
SPACE
MR measurement technique. SPACE is a variant of the 3D Turbo spin echo. As compared to a
conventional TurboSE sequence, SPACE uses
non-selective, short refocussing pulse trains that
consist of RF pulses with variable flip angles. This
allows for very high turbo factors (> 100) and
high sampling efficiency. The results are highresolution, isotropic images that allow for free
reformatting on all levels.
SPAIR
MR measurement technique. Robust fat saturation for body imaging due to a frequency-selective inversion pulse. The SPAIR technique is an
SPAIR:
Spectrally Adiabatic Inversion
Recovery
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alternative for conventional spectral fat saturation and water excitation.
Spatial encoding
MR measurement technique. Definition of
position and orientation of a slice via the frequency and phase-encoding gradient. The location of MR signals is encoded and reconstructed
in subsequent image computations.
Spatial resolution
Image quality. To acquire an image with full spatial resolution, the FoV, the measurement matrix
and the slice thickness have to be considered as
well. It is characterized by the voxel size. The
smaller the voxel, the higher the spatial resolution and the lower the signal measured.
Special coil
–> Local coils
Specific absorption
rate (SAR)
Safety. The RF energy absorbed per time unit
and per kilogram. Absorption of RF energy can
result in warming of the body. Energy absorption
is an important value for establishing safety
thresholds.
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Unauthorized high local concentrations of
RF energy can result in burns (local SAR). When
the RF energy is uniformly distributed, safety
thresholds have to be observed to avoid thermoregulation or cardiac stress (whole-body SAR).
Remedies: other RF pulses, smaller flip angles,
lower TR, fewer slices.
Spectral map
MR spectroscopy. Mapping of a CSI spectral
matrix to an anatomical image. It shows the
regional changes in metabolites as superimposed
contours.
Spectroscopy
–> MR spectroscopy
Spectrum
MR spectroscopy. The frequency plot of the
MR signal. The signal intensity is displayed as a
function of the chemical shift. Nuclei with different resonance frequencies appear as separate
peaks in the spectrum.
Spin
–> Nuclear spin
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Spin density
–> Proton density
Spin-echo (SE)
MR measurement technique. The reappearance of an MR signal after the decay of the FID
signal. Dephasing of the spins (decay in transverse magnetization) is offset through the application of a 180° inversion pulse. The spins
rephase, producing the spin echo at time TE
(echo time).
T2* effects (field inhomogeneity, susceptibility) are reversed but not T2 effects.
Spin-echo sequence
MR measurement technique. The sequence of
an excitation pulse (90°) and refocusing pulse
(180°) produces a spin echo. Can be used to generate strong T2-weighted images.
Spin-lattice relaxation
–> Longitudinal relaxation
Spin-spin coupling
MR spectroscopy. Interaction between MR sensitive nuclei in a molecule, resulting in additional
splitting of peaks in the spectrum.
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Spin-spin relaxation
–> Transverse relaxation
Spoiler gradient
MR measurement technique. Gradient pulse
with sufficient amplitude and/or duration to
completely dephase the transverse magnetization. The spoiler gradient is applied after the
echo so that transverse magnetization is
destroyed prior to the next excitation pulse.
Used for presaturation and FLASH sequences.
SSD
–> Surface shaded display
STEAM technique
MR spectroscopy. Single volume method. With
the STEAM pulse sequence, 3 slice-selective
90° pulses generate a stimulated echo.
Stimulation
Safety. The magnetic field changes quickly when
switching high-field gradients. If the electrical
fields generated exceed a specific threshold,
electrical currents can be induced in the patient's
body.
STEAM:
Stimulated Echo Acquisition
Method
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The currents may lead to peripheral nerve
stimulation for the patient that may be considered uncomfortable.
This is an important value for establishing
safety limits.
STIR sequence
MR measurement technique. Inversion recovery sequence with a short inversion time Tl, used
for fat suppression. TI selection depends on the
field strength.
Stray field
Safety. Magnetic field outside the magnet that
does not contribute to imaging. A specific distance has to be kept between the field and various devices and patients with cardiac pacemakers (e.g., 0.5 mT line).
The stray field is low with permanent magnets
because the system is largely self-shielding.
Stripe tagging
–> Tagging
Superconductive
magnet
MR components. An electromagnet whose
strong magnetic field (typically at least 0.5 T) is
STIR:
Short TI Inversion Recovery
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generated using superconductive coils. The conductive wires of the coils are made of a cryogenically cooled Niobium Titanium alloy. Liquid
helium is used as the cryogen or liquid nitrogen
for pre-cooling.
Superconductivity
Physics. Material characteristic of various alloys,
which at very low temperatures (close to absolute zero) results in a complete loss of electrical
resistance. Electrical current can then flow without loss.
Surface coil
MR components. Special RF receiver coil positioned close to the body to acquire signal from
nearby regions. Compared to the body coil, the
RF receiver coil has a better signal-to-noise ratio
and higher spatial resolution. Surface coils can
also be used for simple localization in MR spectroscopy.
Surface shaded
display (SSD)
Post-processing. Three-dimensional display of
surfaces via variable threshold values, of e.g.,
contrast-enhanced vessels.
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Susceptibility
(Magnetizability)
Physics. Measure for the ability of a material or
tissue to be magnetized in an external magnetic
field.
Susceptibility
artifact
Image quality. Local magnetic field gradients
are produced in all transitions between tissues of
differing magnetic susceptibility. In transitions
between tissue and air-filled spaces (e.g., the
temporal bone), areas may be present that show
reduced signal or no signal at all.
The effect is stronger with gradient echo
sequences, in particular EPI.
Susceptibility contrast
Image quality. T2* contrast
Susceptibilityweighted imaging
(SWI)
MR measurement technique. Susceptibilityweighted imaging displays venous vessels as well
as hemorrhages in the human brain. The SWI
technique reacts with sensitivity to local changes
in magnetic fields caused by desoxygenated
blood or local iron deposits.
SVS method
–> Single volume spectroscopy
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Swap
–> Gradient swap
SWI
–> Susceptibility-weighted imaging (SWI)
syngo
Common imaging software for all Siemens
modalities.
syngo BEAT
–> BEAT
syngo BLADE
–> BLADE
syngo BRACE
–> BRACE
syngo GRACE
–> GRACE
syngo MR
MR-specific syngo application.
syngo NATIVE
–> NATIVE
syngo REVEAL
–> REVEAL
syngo SPACE
–> SPACE
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syngo TimCT
–> TimCT
syngo TWIST
–> TWIST
syngo VIEWS
–> VIEWS
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Tagging
Grid tagging: Grid of saturation lines across
cardiac MR images. Used to view myocardial
motion.
Stripe tagging: Parallel stripes in the MR image;
used to view myocardial motion in primary axis
view or four-chamber view.
Targeted MIP
–> Localized MIP
Tesla (T)
MR physics. SI unit for magnetic field strength.
Approximately 20,000 times as strong as the
earth's magnetic field (1 Tesla = 10000 Gauss).
Tim (Total imaging
matrix)
MR components. The Tim matrix concept allows
for whole-body examinations with an FoV of up
to 205 cm without repositioning the patient. Prerequisites for Tim: matrix coils in combination
with RF receiver channels.
Example: Tim [76 × 32]: Tim system up to
76 coil elements and 32 RF channels
TimCT
MR measurement technique. TimCT (Continuous table move) enables measurements of large
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examination regions with continuous table
move, that is, in one examination step without
measurement pauses or repositioning the table
“MR as easy as CT”. Continuous scanning in the
isocenter of the magnet provides for highest
image quality and avoids slice boundary artifacts
with multi-levels.
Time-of-flight
angiography (ToF)
MR angiography. The time-of-flight angiography (inflow angiography) visualizes vessels
through the flow of non-saturated, fully relaxed
blood into the slice which generates a high signal. By comparison, stationary spins are partially
saturated and generate a relatively low signal
intensity.
–> Inflow amplification
Time series (TS)
Perfusion imaging. The obtained T2* images
are labeled with number and time position in the
series. They maybe used in Cine and for statistical evaluations.
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Time-to-Peak map
(TTP)
Perfusion imaging. A TTP map shows the
regional distribution of the time needed to the
minimum perfusion signal, either in gray scale or
color-coded. It is generated for every slice measured.
TIR sequence
–> Turbo inversion recovery
TIRM sequence
–> Turbo inversion recovery magnitude
Tissue contrast
–> Contrast
t-map
BOLD imaging. When evaluated with the t-test,
the t-map shows the measurement data of BOLD
imaging as strictly functional information. Positive correlations located between stimulation
and active brain areals are shown as bright, negative correlates are shown as dark.
ToF-Angio
–> Time-of-flight angiography
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TONE technique
MR measurement technique. TONE is used for
ToF angiography to minimize the saturation
effects as blood flows through a 3D volume. An
RF pulse with a tilted slab profile compensates
for the velocity and direction of blood flow. This
generates a flip angle that varies from partition
to partition.
Total imaging matrix
–> Tim
Trace image
Diffusion imaging. In Trace images contrast is
generated by the direction of the diffusion tensor. This corresponds to the sum of diagonal elements (trace) of the diffusion tensors:
Trace = Dxx + Dyy + Dzz
Transmission
bandwidth
MR measurement technique. The frequency
range stimulated by the excitation pulse in a
sequence.
Transmitter tuning
MR measurement technique. Setting the transmission power of the RF pulse (flip angle).
TONE:
Tilted, Optimized,
Nonsaturating Excitation
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Transverse
–> Orthogonal slices
Transverse
magnetization (Mxy)
MR physics. Transverse magnetization Mxy is the
component of the macroscopic magnetization
vector in the xy-plane; that is, oriented perpendicular to the applied magnetic field.
The precession of transverse magnetization
induces electrical voltage in a receiver coil that
changes over time. The temporal progression of
this voltage is the MR signal. After RF excitation,
Mxy decays to zero at time constant T2 (ideal) or
T2* (real).
Transverse relaxation
MR physics. Decay of transverse magnetization
through the loss of phase coherence between
precessing spins (due to spin exchange); is also
known as spin-spin relaxation.
Transverse relaxation
time
–> T2 constant
Traveling sat
Slice positioning. A presaturation pulse is
applied to one side of the slice to reduce the sig-
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nal intensity of spins (typically blood) that are
about to flow into this side of the slice. This
enables arteries or veins to be displayed selectively, since the flow is often in the opposite
direction (e.g., carotid artery and jugular vein).
The slices are measured sequentially (slice-byslice). The presaturation pulse retains its position
relative to the slice.
Trigger
Physiologically-controlled imaging. Reference
point in the physiological signal which releases
the scan, e.g., the R wave in the ECG signal.
Trigger delay time (TD)
ECG triggering. Interval between the trigger and
release of the measurement.
Trigger signal
Physiologically-controlled imaging. Physiological signal (ECG signal, finger pulse or respiratory
curve) that starts or restarts data acquisition.
TrueFISP
MR measurement technique. The TrueFISP gradient echo sequence provides the highest signal
of all steady state sequences. The contrast is a
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function of T1/T2. However, with a short TR and a
short TE, the T1 portion remains constant. The
images are primarily T2-weighted.
The FISP and PSIF signal are generated simultaneously. Due to the superposition of both signals, TrueFISP is sensitive to the inhomogeneities
in the magnetic field. The images may contain
interference stripes. For this reason, TR should be
as short as possible, and a shim has to be performed.
Truncation artifact
Image quality. MR images frequently show periodic oscillations parallel to tissue transitions. The
artifacts show bands with alternating high and
lower signal intensity. All abrupt transitions in
tissue are subject to this effect.
The artifact is created through point-by-point
sampling of the analog signal. Theoretically, an
infinite number of points would have to be sampled. In practical application, however, there is a
finite number of points: the data are truncated.
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t-test
BOLD imaging. Statistical evaluation method for
BOLD measurements (previously Z-score). Is used
to compute the differential image from the mean
values of action and non-action images. Today,
the t-test is integrated into GLM.
Turbo factor
Measurement parameters. Measurement time
saved using a TurboSE sequence rather than a
conventional spin-echo sequence.
Example: At a turbo factor of 7, the TurboSE
sequence measures 7 times faster than a
SE sequence with comparable parameters.
TurboFLASH
MR measurement technique. With a TurboFLASH sequence, the entire raw data matrix is
measured in one acquisition only with an ultrafast gradient echo sequence. The image contrast
is modified via preparation pulses.
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Turbo gradient
spin echo
(TurboGSE)
MR measurement technique. With TurboGSE,
additional gradient echoes are generated before
and after each spin echo. The spin echoes are
allocated to the center of the raw data matrix to
give pure T2 contrast. The gradient echoes are
allocated to the outer segments. A pure T2 contrast is obtained by filling these segments. Gradient echoes determine mainly the image resolution.
Advantages as compared to TurboSE: they are
faster, fat is darker, greater sensitivity to susceptibility effects (e.g., bleeding with hemosiderin).
Turbo inversion
recovery
(TurboIR, TIR)
MR measurement technique. TurboSE
sequence with long TEeff to suppress fluids. The
TurboIR sequence allows for a true inversion
recovery display that shows the arithmetic sign
of the signal.
Turbo inversion
recovery magnitude
(TIRM)
MR measurement technique. Identical to
TurboIR, however, with the magnitude image of
the signal and appropriate display.
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Turbo
MR angiography
MR angiography. Fast 3D angio techniques;
increases speed by a factor of 2 using zero filling,
short TR and TE and interpolation techniques in
the slice-selection direction.
Turbo spin echo
(TurboSE, TSE)
MR measurement technique. TurboSE is a fast
multi-echo sequence. Each echo of a pulse train
includes a different phase encoding. Within one
repetition time TR, raw data rows equal to the
number of pulse train echoes are acquired (segmented raw data).
The turbo factor increases speed, and is frequently used to improve resolution.
TWIST
MR measurement technique. The TWIST
method shortens the measurement time for
angiographic examinations even further at high
image quality. This is obtained through an irregular sampling of the raw data lines: the center
lines increase the sampling rate considerably,
increasing the temporal resolution of images.
Bolus timing is not required with TWIST. Also
consumption of contrast agent is reduced.
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T1 constant
(Longitudinal
relaxation time)
MR physics. Tissue-specific time constant which
describes the return of the longitudinal magnetization to equilibrium. After time T1, the longitudinal magnetization grows back to approx. 63 %
of its end value. A tissue parameter that determines contrast.
T1 contrast
Image quality. The contrast of a T1-weighted
image depends primarily on the various T1 time
constants of the different tissue types.
T2 constant
(Transverse
relaxation time)
MR physics. Tissue-specific time constant that
describes the decay of transverse magnetization
in an ideal homogeneous magnetic field. After
time T2, transverse magnetization has lost 63 %
of its original value. A tissue parameter that
determines contrast.
T2 contrast
Image quality. The contrast of a T2-weighted
image depends primarily on the various T2 time
constants of the different tissue types.
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T2* constant
MR physics. Characteristic time constant that
describes the decay of transverse magnetization,
taking into account the inhomogeneity in static
magnetic fields and the human body. T2* is
always less than T2.
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UTE
MR measurement technique. Pulse sequences
with echo times (TE) that are 10–200 shorter
than the conventional ones. This allows for the
display of tissue components with a short T2
(e.g., membranes, compact bone substance)
that could appear as dark only due to their small
signal portion.
UTE:
Ultrashort TE
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venc value
–> Flow sensitivity
Venetian blind artifact
–> Slice boundary artifact
VERSE
MR measurement technique. Sequences with
time-optimized VERSE pulses improve the slice
profile for 3D measurements. This allows for the
accelerated 3D imaging of limited volumes with
a consistent image contrast across the entire
3D slab.
VIBE sequence
MR measurement technique. For reducing the
acquisition time. 3D acquisition with a reduced
number of slices using interpolation and/or partial Fourier techniques, primarily for dynamic
contrast-enhanced examinations of the abdomen.
VIBE:
Volume Interpolated
Breathhold Examination
MR mammography. Bilateral 3D measurement
technique for the breast with fat saturation or
water stimulation.
VIEWS:
Volume Imaging with
Enhanced Water Signal
VIEWS
venc:
velocity encoding
VERSE:
Variable-Rate Selective
Excitation
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Volume of Interest
(VoI)
MR spectroscopy. A VoI is the volume used for
measurements or evaluations.
For SVS or hybrid CSI procedures, VoI means
the measurement volume that supplies the signal. For SVS, VoI and voxel are identical, but for
hybrid CSI the VoI is divided into voxels.
Volume rendering
technique
–> 3D VRT
Voxel
Imaging. Volume element of the sample to be
examined.
Voxel size = slice thickness × pixel size
–> Spatial resolution
Voxel bleeding
MR spectroscopy. Voxel bleeding indicates cross
talk of signal intensities from one voxel to an
adjacent voxel. Up to 10 % of a signal can appear
in an adjacent voxel. These localization artifacts
tend to appear in the image during intensity
tests. It is reduced by an apodization filter (e.g.,
Hanning filter).
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VRT
3D VRT
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Washout effect
Image quality. The washout effect can appear
perpendicular to the image plane during fast
flow. It occurs during spin-echo imaging and similar procedures. Using a 90° pulse, a bolus is
excited within the slice to be measured. If blood
flows out of the slice before the subsequent 180°
pulse, some or all of the signal is lost. This results
in a low signal or no signal at all.
Water image
A pure water image only displays the signal from
water protons in the image and suppresses the
signal from fat protons. Is generated with the
Dixon technique, for example.
Water saturation
Image quality. Frequency-selective excitation of
water, with subsequent dephasing, is used to
suppress water signals. This technique is used for
MR imaging and spectroscopy.
Water suppression
–> Dark-fluid imaging (FLAIR)
–> Water saturation
Whisper
–> Whisper sequences
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Whisper sequences
MR measurement technique. Sequences with
low-noise gradient pulses.
Width
–> Windowing
Windowing
Image display. Settings for brightness (center)
and contrast (width) in the MR image.
Wrap-around
–> Aliasing artifact
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Zero filling
MR measurement technique. Interpolation
technique for expanding a raw data matrix with
zeroes.
ZIP technique
Image reconstruction. Interpolation technique
in the slice-selection direction for 3D measurements. Enables the reconstruction of thinner
slices.
Z-score
–> t-test
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1D PACE
MR measurement technique. Fast motion correction in real time, for example, during cardiac
imaging. This PACE technique allows the patient
to breathe freely during the measurement.
2D PACE
MR measurement technique. The PACE technique used in abdominal imaging is based on a
local 2D test image for motion detection.
3D imaging
MR measurement technique. In 3D imaging the
entire measurement volume, the 3D slab, is stimulated and not just single slices. Additional phase
encoding in the slice-selection direction provides
information in this direction.
3D PACE
MR measurement technique. Fully automatic
technique for motion detection and correction
during BOLD measurements. Serves to eliminate
motion artifacts.
3D PACE corrects 6 degrees of freedom
(3 translations and 3 rotations) in real time.
PACE:
Prospective Acquisition
Correction
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3D shim
Quality assurance. 3D shim enables the shim
volume to be limited (local shim). A 3D volume
(VoI) is defined. The local magnetic field distribution is determined in this volume, resulting in the
calculation of the shim currents.
A 3D shim provides for a more precise result
than a MAP shim and therefore for a better fat
saturation. For spectroscopy, it provides a better
starting value for the interactive shim.
3D slab
Measurement parameters. Measurement volume stimulated for 3D imaging. The 3D slab is
divided into partitions.
3D TurboSE
MR measurement technique. As a 3D
sequence, TurboSE allows for the acquisition of
T2 images with thin slices and practically uniform
voxels.
3D VRT
Post-processing. 3D display for well-defined
imaging of complex anatomies and anatomic
relationships, e.g., in contrast angiography. In
VRT:
Volume Rendering Technique
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addition to color images, a threshold-based segmentation of 3D objects is possible.
Abbreviations
ADC
ADC
ART
AS
ASL
b
B
BRACE
B0
B1
CE MRA
CM
CNR
CP
CSF
CSI
dB/dt
DTI
EPI
FA
FA
FFT
FID
Analog-to-Digital Converter
Apparent Diffusion Coefficient
Advanced Retrospective Technique
Active Shielding
Arterial Spin Labeling
b-value
Magnetic induction, MR: Magnetic field
Breast Acquisition Correction
Main magnetic field
Alternating magnetic field
Contrast-Enhanced MR Angiography
Contrast agent
Contrast-to-Noise Ratio
Circular Polarization
Cerebro-Spinal Fluid, Liquor
Chemical Shift Imaging
Temporal change of he magnetic field
Diffusion Tensor Imaging
Echo-Planar Imaging
Flip Angle
Fractional Anisotropy
Fourier Transformation
Free Induction Decay
Abbreviations
FLAIR
fMRI
FoV
FT
FWHM
GBP
GLM
GMR
GRACE
GRAPPA
GRE
GSP
Hz
IPA
iPAT
IPP
IR
IRM
LP
MDDW
MIP
MPPS
Fluid Attenuated Inversion Recovery
Functional Magnetic Resonance Imaging
Field of View
Fourier Transformation
Full-Width at Half-Maximum (Peak)
Global Bolus Plot
General Linear Model
Gradient Motion Rephasing, flow compensation
Generalized Breast Spectroscopy Exam
Generalized Autocalibrating Partially Parallel
Acquisition
Gradient Echo
Graphical Slice Positioning
Hertz
Integrated Panoramic Array
Integrated Parallel Acquisition Techniques
Integrated Panoramic Positioning
Inversion Recovery
inversion Recovery Magnitude
Linear Polarization
Multi-Directional Diffusion Weighting
Maximum Intensity Projection
Modality Performed Procedure Step
Abbreviations
MPR
MR
MRA
MRI
MRS
mSENSE
MTC
mT/m
MTT
Mxy
MZ
NMR
PACE
PAT
PBP
PCA
ppm
RARE
RF
RoI
SAR
SE
SENSE
Multi-Planar Reconstruction
Magnetic Resonance
MR Angiography
Magnetic Resonance Imaging
MR Spectroscopy
Modified Sensitivity Encoding
Magnetization Transfer Contrast
Millitesla per meter
Mean Transit Time
Transverse magnetization
Longitudinal magnetization
Nuclear Magnetic Resonance
Prospective Acquisition Correction
Parallel Acquisition Techniques
Percentage of Baseline at Peak
Phase-Contrast Angiography
Parts per million
Rapid Acquisition with Relaxation Enhancement
Radio Frequency
Region of Interest
Specific Absorption Rate
Spin-Echo
Sensitivity Encoding
Abbreviations
SI
SLINKY
SMASH
SNR
SPAIR
SPIDER
SR
SSD
SVS
SWI
T
TA
TD
TE
TEeff
TGSE
TI
Tim
TimCT
TIR
TIRM
TR
Système Internationale
Sliding Interleaved ky
Simultaneous Acquisition of Spatial Harmonics
Signal-to-Noise Ratio
Spectrally Adiabatic Inversion Recovery
Steady-State Projection Imaging with Dynamic
Echo-Train Readout
Saturation Recovery
Surface Shaded Display
Single Volume Spectroscopy
Susceptibility-Weighted Imaging
Tesla
Acquisition time
Delay time
Echo time
Effective echo time
Turbo Gradient Spin-Echo
Inversion time
Total imaging matrix
Tim Continuous Table move
Turbo Inversion Recovery
Turbo Inversion Recovery Magnitude
Repetition time
Abbreviations
TReff
TSE
TTP
UTE
venc
VERSE
VIBE
VIEWS
VoI
VRT
Effective repetition time
Turbo Spin-Echo (TurboSE)
Time To Peak
Ultrashort TE
Velocity encoding
Variable-Rate Selective Excitation
Volume Interpolated Breathhold Examination
Volume Imaging with Enhanced Water Signal
Volume of Interest
Volume Rendering Technique
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© Siemens AG 2008
Order number
MR-00000.640.02.01.02
Printed in Germany
01/2008
Siemens AG
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Germany
www.siemens.com/medical
Contact:
Siemens AG
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Telephone: +49 9131 84-0